Load all coordinates when creating windowed arrays

[RanaPriyansh]

Description

Load all dataset coordinates when to_windowed_arrays runs. Keep eager loading for lon, lat, and depth data variables. Add a regression test for coordinate values and windowed field storage.

Verification

• 18 tests passed in tests/test_windowed_array.py.
• 7 focused interpolation tests passed.
• Ruff lint and format checks passed.
• Mypy reported 163 errors in 13 files. The exact base commit reports the same errors.

Checklist

• Closes Load all coordinates in from_windowed_arrays #2885
• Tests added
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it: Codex used.