Enrich waterdata getter docstrings with examples adapted from R

[thodson-usgs]

Summary

Cross-referenced each Python waterdata getter's Examples section against the corresponding R analogue in DOI-USGS/dataRetrieval and ported the distinctive examples that the Python docs were missing. Same rationale as the audit done for get_combined_metadata in #264 — many R example sets cover useful idioms (ISO 8601 durations, half-bounded time intervals, last_modified for incremental polling, multi-value POST queries) that aren't yet shown in the Python docs.

Docs only — no signature, behavior, or test changes.

Functions touched and what was added

Function	Added
get_daily	ISO 8601 duration (time="P7D") example; last_modified="P7D" example for incremental ETL polling. Also fixed a pre-existing bug where the multi-site / approval_status example block was missing its closing parenthesis and trailing comma.
get_latest_continuous	time="P7D" example (drops sites with no recent observation); multi-site / multi-parameter + last_modified="P7D" example.
get_latest_daily	last_modified="P7D" example; multi-site + multi-parameter (discharge + water-temperature) example.
get_field_measurements	Half-bounded time example ("1980-01-01/.." for everything since 1980; documents the inverse "../<date>" form).

What was deliberately skipped

• Functions whose example coverage already matched or exceeded R's: get_continuous (5 examples), get_monitoring_locations (2 well-chosen ones already, R's bbox+chaining cases would duplicate get_combined_metadata's new chaining example in Add waterdata.get_combined_metadata for combined location + time-series inventory #264), get_time_series_metadata, get_stats_por, get_stats_date_range, get_samples, get_codes, get_reference_table, get_channel, get_samples_summary.
• R-only kwargs that have no Python equivalent (no_paging, attach_request, chunk_size, convertType flag toggling). Filter chunking happens automatically in Python.
• get_daily's R dv_post example using approval_status=c("Approved", "Provisional") — Python already has an approval_status="Approved" example.

Test plan

• ruff check clean.
• Each function's __doc__ renders correctly (verified via help()).
• Live API spot-check: attempted but blocked by a 429 rate limit. The new examples only exercise date-format and multi-value idioms (P7D duration, 1980-01-01/.. half-bounded interval, last_modified field) that are already covered by existing tests and other functions' working examples.

Related

• Add waterdata.get_combined_metadata for combined location + time-series inventory #264 (added get_combined_metadata with the same docs philosophy applied to a single new function).