feat: add joystick widget for virtual control with deflection signals

[tlambert03]

playing with a new way to move the stage. A joystick pad that moves in a vector, with a given velocity, based on a clicked mouse position, relative to the origin. With a quadratic response curve (more control towards the center)

Untitled.mov

[codecov]

Codecov Report

❌ Patch coverage is 26.17450% with 110 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.22%. Comparing base (b4a9089) to head (0afb96c).

Files with missing lines	Patch %	Lines
src/pymmcore_widgets/control/_joystick.py	25.67%	110 Missing ⚠️

❌ Your patch check has failed because the patch coverage (26.17%) is below the target coverage (85.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #512      +/-   ##
==========================================
- Coverage   87.89%   87.22%   -0.68%     
==========================================
  Files         115      116       +1     
  Lines       13727    13876     +149     
==========================================
+ Hits        12066    12103      +37     
- Misses       1661     1773     +112     

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[fdrgsp]

It would be cool to add it directly over the preview viewer in pymmcore-gui so that we can use it to move the stage when in live mode 😁

[tlambert03]

yeah!