draft: simplify slice overloads

[randolf-scholz]

This drops the "None as Any" assumption in the slice.__new__ overloads, fixing #15526.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

kornia (https://github.com/kornia/kornia)
+ kornia/geometry/subpix/nms.py:135: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ kornia/models/sam/architecture/mask_decoder.py:112: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]

freqtrade (https://github.com/freqtrade/freqtrade)
+ freqtrade/exchange/exchange.py:3341: error: Argument 1 to "slice" has incompatible type "None"; expected "int"  [arg-type]

xarray (https://github.com/pydata/xarray)
+ xarray/core/dataset.py: note: In member "tail" of class "Dataset":
+ xarray/core/dataset.py:3227: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ xarray/core/dataset.py: note: In member "diff" of class "Dataset":
+ xarray/core/dataset.py:7870: error: Incompatible types in assignment (expression has type "dict[Hashable, slice[None, int, None]]", variable has type "dict[Hashable, slice[int, None, None]]")  [assignment]
+ xarray/computation/rolling.py: note: In member "_numbagg_reduce" of class "DataArrayRolling":
+ xarray/computation/rolling.py:624: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ xarray/computation/rolling.py: note: In member "_bottleneck_reduce" of class "DataArrayRolling":
+ xarray/computation/rolling.py:669: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ xarray/tests/test_backends.py: note: In member "test_write_region_mode" of class "ZarrBase":
+ xarray/tests/test_backends.py:3520: error: No overload variant of "to_zarr" of "Dataset" matches argument types "Any", "object", "Any", "dict[str, Any]"  [call-overload]
+ xarray/tests/test_backends.py:3520: note: Possible overload variants:
+ xarray/tests/test_backends.py:3520: note:     def to_zarr(self, store: Any | None = ..., chunk_store: MutableMapping[Any, Any] | str | PathLike[Any] | None = ..., mode: Literal['w', 'w-', 'a', 'a-', 'r+', 'r'] | None = ..., synchronizer: Any = ..., group: str | None = ..., encoding: Mapping[Any, Any] | None = ..., *, compute: Literal[True] = ..., consolidated: bool | None = ..., append_dim: Hashable | None = ..., region: Mapping[str, slice[Any, Any, Any] | Literal['auto']] | Literal['auto'] | None = ..., safe_chunks: bool = ..., align_chunks: bool = ..., storage_options: dict[str, str] | None = ..., zarr_version: int | None = ..., zarr_format: int | None = ..., write_empty_chunks: bool | None = ..., chunkmanager_store_kwargs: dict[str, Any] | None = ...) -> ZarrStore
+ xarray/tests/test_backends.py:3520: note:     def to_zarr(self, store: Any | None = ..., chunk_store: MutableMapping[Any, Any] | str | PathLike[Any] | None = ..., mode: Literal['w', 'w-', 'a', 'a-', 'r+', 'r'] | None = ..., synchronizer: Any = ..., group: str | None = ..., encoding: Mapping[Any, Any] | None = ..., *, compute: Literal[False], consolidated: bool | None = ..., append_dim: Hashable | None = ..., region: Mapping[str, slice[Any, Any, Any] | Literal['auto']] | Literal['auto'] | None = ..., safe_chunks: bool = ..., align_chunks: bool = ..., storage_options: dict[str, str] | None = ..., zarr_version: int | None = ..., zarr_format: int | None = ..., write_empty_chunks: bool | None = ..., chunkmanager_store_kwargs: dict[str, Any] | None = ...) -> Any
+ xarray/tests/test_backends.py:3520: error: Argument 1 to "isel" of "Dataset" has incompatible type "object"; expected "Mapping[Any, Any] | None"  [arg-type]

static-frame (https://github.com/static-frame/static-frame)
+ static_frame/core/node_selector.py:828: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ static_frame/core/type_blocks.py:3665: error: Argument 2 to "slice" has incompatible type "None"; expected "int"  [arg-type]
+ static_frame/core/type_blocks.py:3667: error: Incompatible types in assignment (expression has type "slice[None, None, None]", variable has type "slice[int, int, None]")  [assignment]
+ static_frame/core/type_blocks.py:3741: error: Argument 2 to "slice" has incompatible type "None"; expected "int"  [arg-type]
+ static_frame/core/type_blocks.py:3743: error: Incompatible types in assignment (expression has type "slice[None, None, None]", variable has type "slice[int, int, None]")  [assignment]
+ static_frame/core/type_blocks.py:4023: error: Argument 2 to "slice" has incompatible type "None"; expected "int"  [arg-type]
+ static_frame/core/series.py:1714: error: Argument 2 to "slice" has incompatible type "None"; expected "int"  [arg-type]
+ static_frame/core/series.py:1716: error: Incompatible types in assignment (expression has type "slice[None, None, None]", variable has type "slice[int, int, None]")  [assignment]
+ static_frame/core/quilt.py:170: error: Incompatible types in assignment (expression has type "IndexBase", target has type "Index[Any] | TTreeNode")  [assignment]

pandas (https://github.com/pandas-dev/pandas)
+ pandas/core/array_algos/transforms.py:39: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ pandas/core/array_algos/transforms.py:41: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1396: error: Argument 2 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1396: error: Argument 1 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1396: error: Argument 2 to "slice" has incompatible type "None"; expected "int | integer[Any]"  [arg-type]
+ pandas/core/algorithms.py:1407: error: Argument 1 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1407: error: Argument 1 to "slice" has incompatible type "None"; expected "int | integer[Any]"  [arg-type]
+ pandas/core/algorithms.py:1407: error: Argument 2 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1411: error: Argument 2 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1411: error: Argument 1 to "slice" has incompatible type "int | integer[Any]"; expected "None"  [arg-type]
+ pandas/core/algorithms.py:1411: error: Argument 2 to "slice" has incompatible type "None"; expected "int | integer[Any]"  [arg-type]

scipy (https://github.com/scipy/scipy)
+ scipy/optimize/_isotonic.py:124: error: Argument 3 to "slice" has incompatible type "int"; expected "None"  [arg-type]

jax (https://github.com/google/jax)
+ jax/_src/numpy/lax_numpy.py:573: error: Argument 3 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/_src/numpy/lax_numpy.py:1662: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/_src/numpy/lax_numpy.py:1663: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:1999: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:1999: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:1999: error: Argument 3 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2000: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2000: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2000: error: Argument 3 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2004: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2004: error: Argument 2 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/sparse/bcoo.py:2004: error: Argument 3 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/mosaic/gpu/launch_context.py:199: error: Argument 1 to "slice" has incompatible type "int"; expected "None"  [arg-type]
+ jax/experimental/mosaic/gpu/fragmented_array.py:3940: error: Argument 1 to "slice" has incompatible type "None"; expected "int"  [arg-type]

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/web_request.py:599:22: error: Argument 1 to "slice" has incompatible type "Any | None"; expected "int"  [arg-type]
+ aiohttp/web_request.py:599:29: error: Argument 2 to "slice" has incompatible type "Any | None"; expected "int"  [arg-type]