BUG: Fix ValueError when plotting DataFrame with descending DatetimeI…

[anubhav9369]

• closes BUG: DataFrames with backwards time index cannot be plotted #64819
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v3.1.0.rst file if fixing a bug or adding a new feature.
• I have reviewed and followed all the contribution guidelines
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

[anubhav9369]

All failures are due to the pre-existing flaky test test_no_track_times (GH#32682) in test_store.py, which checks HDF5 file checksums based on timing unrelated to this plotting fix. This test was already failing on main before this PR.

[anubhav9369]

macOS py312 runs 223k tests with 0 failures.
Happy to rebase or make any changes the maintainers suggest.

[ayshih]

Presumably this PR has been superseded by the now-merged #64946 and should be closed

[jorisvandenbossche]

Indeed, @anubhav9369 apologies for not getting you a review on time!