Fix: axes aspect shifting on pixel snapping after drawn

[cvanelteren]

Closes#679 by restoring alignment for mixed-span subplot layouts when one one of the axes uses a fixed aspect ratio. The regression showed up in arrangements like [[1, 2], [1, 3]], where an equal-aspect axis on the left would shrink inside its gridspec slot but the stacked axes on the right would keep their full vertical extent and visibly stick out above and below it. This change teaches the figure layout pass to propagate the aspect-constrained bounds across the neighboring subplots that share the same span, and adds a regression test for both the legacy and UltraLayout code paths so the layout stays visually consistent going forward.

[codecov]

Codecov Report

❌ Patch coverage is 96.35922% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ultraplot/figure.py	85.14%	10 Missing and 5 partials ⚠️

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[cvanelteren]

need to fix the code patch and refactor some of this but otherwise LGTM.

[Copilot]

Pull request overview

Fixes a regression where mixed-span subplot mosaics (e.g. [[1, 2], [1, 3]]) become visually misaligned after draw when a spanning axes uses a fixed aspect ratio, by propagating the aspect-constrained bounds to adjacent sibling subplots.

Changes:

• Add Figure._align_aspect_constrained_axes() to remap sibling subplot slots onto the post-apply_aspect() box for spanning fixed-aspect axes.
• Invoke the new alignment step during Figure.auto_layout() after both the aspect and tight layout passes.
• Add a regression test covering both legacy and UltraLayout code paths.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ultraplot/figure.py	Adds aspect-constrained span alignment logic and integrates it into the auto-layout pipeline.
ultraplot/tests/test_ultralayout.py	Adds regression coverage for the mixed-span + fixed-aspect alignment behavior across layout engines.

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[cvanelteren]

Regression is not caused by this PR -- merging.