fix: Add regression tests for Heatmaps IndexError fix (PR #6438)

[Azaya89]

Closes #6232

This PR adds tests to verify that IndexError is properly suppressed when mouse/tap events occur outside the bounds of categorical axes on plots like HeatMaps, preventing crashes when users hover/click outside the plots or on colorbars or legends.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.22%. Comparing base (1005798) to head (25672c1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6708      +/-   ##
==========================================
+ Coverage   89.19%   89.22%   +0.02%     
==========================================
  Files         332      332              
  Lines       71928    72041     +113     
==========================================
+ Hits        64158    64275     +117     
+ Misses       7770     7766       -4     

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[hoxbro]

I feel like the tests are too synthetic. Could we instead make a UI test that recreates the problem in #6232

[Azaya89]

I feel like the tests are too synthetic. Could we instead make a UI test that recreates the problem in #6232

Are you suggesting I replace the tests with something like the MRE in #6232 or just add the UI tests to these ones already written?

[hoxbro]

I think we should replace the existing tests with a UI test.

[hoxbro]

We should verify that these tests fails, if we are running without the fix in #6438