ENH: list NOAA atmosphere datasets and fetch latest (#660)

[thatrandomasiandev]

Summary

• Adds best-effort helpers to list NCEP atmosphere collections and per-collection run identifiers from the Unidata THREDDS catalogs RocketPy already uses for GFS/NAM/RAP/HRRR/AIGFS (list_noaa_atmosphere_datasets, list_noaa_dataset_identifiers).
• Adds convenience APIs to resolve and open the latest collection run via OPeNDAP (get_latest_noaa_opendap_url, fetch_latest_noaa_dataset) without changing Environment.
• Documents limitations: NOMADS OPeNDAP is retired, so discovery scrapes THREDDS XML catalogs (layout can change); “download” means opening the remote dataset handle (same pattern as existing fetchers), not writing a local GRIB file.

Fixes #660

Test plan

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python -m pytest tests/unit/environment/test_fetchers.py -q (25 passed; catalog/HTTP mocked, no live NOAA)