docs(examples): migrate demo notebooks to the Water Data API

Port the example notebooks still using the deprecated nwis module onto waterdata and re-execute them against the live API:
- Statistics  -> get_stats_date_range / get_stats_por
- Peaks       -> get_peaks
- Ratings     -> get_ratings
- NWIS_demo_1 -> get_peaks (and get_monitoring_locations in the trend analysis)
- R Python Vignette equivalents -> get_monitoring_locations / get_daily / get_continuous / get_samples / get_peaks / get_ratings / get_stats_date_range
WaterUse stays on the now-defunct nwis.get_water_use with a prominent note that USGS water-use data has no Water Data API equivalent. The remaining Hydroshare notebooks were already on waterdata.

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

Author: thodson-usgs