Italy toscany

[thiagovmdon]

Summary

Related to issue #101

This PR adds support for Italy-Toscany via the public Regione Toscana SIR hydrological services.

Implemented in this PR:

• add ItalyToscanyFetcher
• support discharge_daily_mean
• support stage_daily_mean
• integrate the new fetcher into rivretrieve/__init__.py
• add cached station metadata
• add example usage
• add unit tests with sample metadata and archive payloads
• add fetcher documentation and wire it into the Sphinx API reference

Implementation notes:

• live metadata merges the public geo:cf_idrometri WFS layer with the public SIR monitoring station table
• coordinates are transformed from EPSG:3003 to WGS84
• daily discharge is downloaded from the archive endpoint with IDST=idro_p
• daily stage is downloaded from the archive endpoint with IDST=idro_l
• archive CSVs are parsed from semicolon-separated, decimal-comma provider files
• discharge availability varies by station, so stations without archived flow data return an empty DataFrame for discharge requests