Fix: Handle DateIndex in CSA plot_data to resolve crash (fixes #1864)

[shivamlalakiya]

Description

I updated the plotting logic in mv_its.py to use direct matplotlib calls instead of pandas.plot(). This fixes a crash that occurs when the input data has a DatetimeIndex, as reported in issue #1864.

Changes included:

• Replaced data.plot(ax=ax) with ax.plot(data.index, data.values).
• Added a regression test in tests/customer_choice/test_mv_its.py to verify that plotting with a DateIndex no longer errors.

Related Issue

• Closes data with date index doesn't plot correctly #1864
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass. Feel free to comment pre-commit.ci autofix to auto-fix.
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks) using numpydoc format.
• If you are a pro: each commit corresponds to a relevant logical change

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📚 Documentation preview 📚: https://pymc-marketing--2302.org.readthedocs.build/en/2302/

[cursor]

PR Summary

Low Risk
Small plotting-only change with a focused regression test; minimal impact outside visualization behavior (legend/line rendering).

Overview
Fixes a crash in MVITS.plot_data/plot_product when the input has a DatetimeIndex by replacing pandas.DataFrame.plot() usage with explicit matplotlib ax.plot(...) calls per column, and always adding a legend.

Adds a regression test (test_plot_data_with_datetime_index) to ensure plotting works for time series indexed by dates.

^{Written by Cursor Bugbot for commit 81e7f4f. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.05%. Comparing base (43f39c7) to head (81e7f4f).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2302   +/-   ##
=======================================
  Coverage   93.05%   93.05%           
=======================================
  Files          78       78           
  Lines       12228    12230    +2     
=======================================
+ Hits        11379    11381    +2     
  Misses        849      849           

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