fix: anchor EVM roots by multihash digest

[eloramirez1356]

Summary

This PR fixes EVM self-anchoring for Ceramic roots whose encoded CID prefix is not a fixed length.

The main bug was in cid_to_bytes32: it previously sliced the encoded CID bytes assuming a fixed 4-byte prefix before passing the value to anchorDagCbor(bytes32 root). That works for some CIDs, but fails for others because CID prefixes are varint-encoded and their length is not stable across codecs / wrappers.

This PR changes anchoring to extract the raw multihash digest directly and updates validation to compare the committed multihash digest, which is what the on-chain f(bytes32) proof format actually commits.

What changed

Anchoring fix

• update anchor-evm/src/evm_transaction_manager.rs to derive the bytes32 root from cid.hash().digest() instead of slicing encoded CID bytes
• add a regression test covering variable-length CID prefixes

Validation fix

• update event-svc/src/event/validator/time.rs to compare root multihashes rather than requiring full CID equality
• add a test showing validation succeeds when two root CIDs use different wrappers but preserve the same multihash digest

Debugging / observability

• add targeted debug logging in:
  • anchor-evm/src/proof_builder.rs
  • anchor-service/src/merkle_tree.rs
  • anchor-evm/src/evm_transaction_manager.rs

Documentation

• update anchor-evm/README.md to explain the bytes32 root semantics and why digest-based extraction / comparison is required

Why this is needed

The contract interface is:

function anchorDagCbor(bytes32 root) external;

Additional cleanup

The first commit contains a few small unrelated fixes required to pass the repository's current make build / make check-clippy / make check-fmt checks:

• remove an unused struct in anchor-remote
• add a scoped clippy::large_enum_variant allow in event
• simplify a clippy-reported conditional in pipeline
• apply a formatting fix in event-svc