Fix categorical pyplot gallery rendering [mpl compatibility]

[sselvakumaran]

Summary

• map pyplot categorical coordinates to first-seen ordinal positions while computing view limits, matching the core's category mapping
• support Matplotlib's per-patch bar(..., label=[...]) legend semantics, including underscore filtering and each patch's resolved color
• keep bar geometry vectorized and add focused gallery regression coverage for categorical trajectories, legends, and barh widths

Root causes

Pyplot's pre-build autoscale scan discarded string coordinates, so categorical line and scatter plots fell back to a dataless (0, 1) view and clipped every category after the second. Separately, a sequence passed as a bar label was stringified as one container label instead of being attached to the individual bar patches.

Visual comparison

Columns are Matplotlib 3.11, the branch base, and this PR. The first row shows the per-bar legend fix; the second shows all six categorical trajectories restored.

Validation

• PYTHONPATH=python /Users/srimans/dev/reviz/.venv/bin/python -m pytest -q tests/pyplot/test_categorical_gallery_regressions.py — 5 passed
• PYTHONPATH=python /Users/srimans/dev/reviz/.venv/bin/python -m pytest -q tests/pyplot — 558 passed, 65 skipped
• Ruff check and format check pass
• exact Matplotlib 3.11 gallery sources rendered for bar_colors.py and categorical_variables.py

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• Commit unit tests in branch agent/categorical-geometry-gallery-compat

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[codspeed-hq]

Merging this PR will degrade performance by 39.52%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 101 untouched benchmarks
⏩ 1 skipped benchmark¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	test_build_bar_categorical_pyplot	4.3 ms	7.2 ms	-39.52%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing agent/categorical-geometry-gallery-compat (40adc1e) with agent/fix-pyplot-autoscale-margins (3b3c2ab)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[sselvakumaran]

maybe a problem solved by another PR - labels should ideally go where there is no lines if possible; like the label here should go in the upper left or lower right of the graph. otherwise this specific fix works.