refactor(waterdata): rename include_hash_ids to include_hash; tighten docs

Rename the opt-in flag include_hash_ids -> include_hash across the OGC
getters, get_samples, get_stats_*, the internal helpers, and the tests.
The flag is new in this PR (never on main), so this is not a breaking
change. Collapse the per-getter docstrings to two lines.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thodson-usgs