Fix duplicate shared boxplot tick labels

[cvanelteren]

This fixes the shared-axis boxplot regression where repeated boxplot calls on axes with sharex >= 2 could append the same fixed tick labels multiple times, making the x tick labels appear duplicated or bold. The boxplot wrapper now avoids Matplotlib's appending tick manager on already shared axes and applies the intended tick labels once, with a regression test covering the reported case. Closes #628.

[Copilot]

Pull request overview

Fixes a regression in UltraPlot’s boxplot wrapper where repeated boxplot() calls on axes with stronger x-axis sharing (sharex >= 2) could accumulate duplicate fixed tick labels, causing duplicated/bold x tick label rendering. Adds a regression test for the reported scenario (issue #628).

Changes:

• Add shared-axis detection for boxplot tick management and bypass Matplotlib’s appending tick-manager on shared tickers.
• Install fixed tick locator/formatter once per call for shared axes to prevent duplicated tick labels.
• Add a regression test ensuring shared x axes do not end up with duplicated tick label text.

Reviewed changes

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

File	Description
ultraplot/axes/plot.py	Avoid Matplotlib’s tick-manager path on shared tick axes and apply fixed ticks/labels without duplication.
ultraplot/tests/test_plot.py	Adds regression test covering repeated boxplot calls under sharex=2 to ensure tick labels don’t duplicate.

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[cvanelteren]

Manual inspection looks good. Merging.