fix: prevent data race with cursedRenderer.onMouse

[lrstanley]

Changes in this PR

Fixes a data race in the cursed renderers OnMouse handler. Opted to capture just the handler, rather than duplicating the reference to keep the intent clear.

• closes bug: data race between received mouse events and using cursed renderer #1690
• Added -race, -count, and -cpu to taskfile. Ideally, more people should run with these tests to help cover more data race testing, flaky tests, as well as tests which may not actually surface issues unless the CPU > 1, and vice versa.
• Added t.Parallel() (to root or within t.Run()) to all viable tests that don't do any global state or similar mutations.
• Fixed examples/go.mod & examples/go.sum not being in sync, though unrelated to my change.

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• I have read CONTRIBUTING.md.

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.50%. Comparing base (640d879) to head (04ceac4).

Files with missing lines	Patch %	Lines
cursed_renderer.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1691      +/-   ##
==========================================
+ Coverage   55.64%   56.50%   +0.85%     
==========================================
  Files          25       25              
  Lines        1310     1315       +5     
==========================================
+ Hits          729      743      +14     
+ Misses        491      482       -9     
  Partials       90       90              

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