feat(bass): plotting methods for BassModel

[anevolbap]

Related Issue

• Closes Plotting methods for BassModel #2589
• Related to Dual y-axes for the "Innovators vs Imitators" plots in bass notebook #1706

Description

Adds the four plotting methods from #2589 to BassModel, built on pymc_marketing.plot.plot_curve so the visuals match the rest of the library:

• plot_adoption_curve: posterior new adopters per period with HDI, observed counts overlaid.
• plot_cumulative: cumulative adoption S-curve with HDI, observed cumulative overlaid.
• plot_decomposition: innovators and imitators per period on the left y-axis, cumulative adoption on a twin right y-axis. This is the dual-axes design requested in Dual y-axes for the "Innovators vs Imitators" plots in bass notebook #1706; that issue can close once the notebook adopts this method in Update Bass notebook to use BassModel class #2590.
• plot_peak: posterior of the peak adoption time via arviz.plot_posterior.

All functions live in a new pymc_marketing.bass.plotting module and are exposed both as module functions and as plot_* methods on BassModel. Multi-product models render one subplot per product; product="A" selects a single one. Each function returns (fig, axes), so mlflow.log_figure works directly with the autolog workflow from #2624.

The branch includes the matplotlib<3.11 pin from #2626 so CI can run; it drops out once that PR merges.

Checklist

• Checked that the pre-commit linting/style checks pass
• 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

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📚 Documentation preview 📚: https://pymc-marketing--2628.org.readthedocs.build/en/2628/

[codecov]

Codecov Report

❌ Patch coverage is 98.91304% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.22%. Comparing base (649547e) to head (3d97174).

Files with missing lines	Patch %	Lines
pymc_marketing/bass/plotting.py	98.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2628      +/-   ##
==========================================
+ Coverage   94.19%   94.22%   +0.02%     
==========================================
  Files         100      101       +1     
  Lines       15384    15476      +92     
==========================================
+ Hits        14491    14582      +91     
- Misses        893      894       +1     

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