Add coordinate reference system (CRS) support to acoustic localization

[martinguthrie93]

Summary

Adds optional coordinate reference system (CRS) support to the localization module,
so users can work directly with geographic coordinates (longitude/latitude) instead of
manually projecting to meters. Closes #1262.

What changed

• New opensoundscape/localization/coordinates.py with pyproj-backed helpers:
  utm_epsg_for_lonlat, lonlat_to_xy, xy_to_lonlat, project_file_coords.
• SynchronizedRecorderArray: new from_lonlat() classmethod that projects lon/lat
  receiver coordinates to a metric CRS (auto-selects the UTM zone), plus a crs
  attribute propagated to each returned PositionEstimate.
• PositionEstimate: new crs field and location_estimate_lonlat property that
  converts the estimated location back to longitude/latitude.
• pyproj added as an optional dependency + localization extra
  (pip install opensoundscape[localization]). Core install is unaffected.

Why

Field recorders log positions as lon/lat (WGS84), but localization requires Cartesian
meters. Previously users had to manually pick a UTM zone and convert coordinates by
hand (error-prone). This makes the lon/lat → localization → mapped-result path direct.

Testing

• New tests/test_coordinates.py (12 tests): round-trip conversion, UTM zone
  selection (N/S hemisphere), from_lonlat, location_estimate_lonlat, dict
  round-trip. Skipped automatically if pyproj is not installed.
• All existing localization tests still pass (47 passed locally).
• black formatting applied.