Fix tiny wx plot window on wxPython 4.3

[adarshsm]

PR summary

Fixes #32143 — with wxPython 4.3 / 4.3.1 the WxAgg plot window opens tiny (~132×131) and must be manually resized; wxPython 4.2.5 is unaffected.

Cause

In FigureFrameWx.__init__ (lib/matplotlib/backends/backend_wx.py):

self.canvas.SetInitialSize(self.FromDIP(wx.Size(w, h)))  # sets size AND min size to (w, h)
self.canvas.SetMinSize(self.FromDIP(wx.Size(2, 2)))      # resets min size to (2, 2)
self.canvas.SetFocus()

self.Fit()                                               # sizes the frame from the canvas

SetInitialSize(w, h) sets both the size and the min size to (w, h), but the next line resets the canvas min size to (2, 2), and only then is Fit() called. wxPython 4.3 tracks wxWidgets 3.3, where Fit() sizes the frame from the canvas's current min size — so the (2, 2) reset collapses the window. wxPython 4.2.5 (wxWidgets 3.2) honoured the initial size instead.

Fix

Call Fit() while the canvas min size is still the initial (w, h), then relax it to (2, 2) afterwards so the window can still be resized smaller.

Testing

This is GUI-backend window sizing, which isn't covered by the automated suite. The issue reporter tested this exact reorder and confirmed it:

Thanks a lot for investigating. I can confirm that this works!

— #32143 (comment) (and their confirmation).

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[adarshsm]

Heads up on the one red check: codecov/patch is failing because the change is in FigureFrameWx.__init__, which is wx GUI-backend code that CI can't exercise for coverage — so the reordered lines report 0% patch coverage. Those two statements (self.Fit() and the SetMinSize call) were already uncovered before this PR; the change only reorders existing lines rather than adding new untested logic.

I don't think a regression test is feasible here: the bug only manifests on wxPython 4.3 (wxWidgets 3.3) with a real display. On the wx 4.2.x available in CI, both the old and new ordering produce a correctly-sized window, so a test would pass regardless of the fix and wouldn't actually guard the regression. The verification is the issue reporter confirming the reorder resolves the tiny-window behaviour on wx 4.3 (#32143). Happy to adjust if you'd prefer a different approach.

[QuLogic]

Can't test, but seems reasonable if the original reporter confirmed it worked.