feat: Add better support for stylus hovering

[3akev]

This PR adds handlers for hovering stylus events, which are used to switch to the eraser tool when the stylus button is pressed while hovering.

This replaces the old functionality where pressing the stylus button mid-stroke removes the stroke, making it more in-line with other note applications and (in my opinion) more user friendly.

Closes #859

[codecov]

Codecov Report

Attention: Patch coverage is 29.41176% with 12 lines in your changes missing coverage. Please review.

Project coverage is 47.19%. Comparing base (94c176f) to head (9f1f9ac).

Files with missing lines	Patch %	Lines
lib/pages/editor/editor.dart	30.00%	7 Missing ⚠️
lib/components/canvas/canvas_gesture_detector.dart	28.57%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1355      +/-   ##
==========================================
- Coverage   47.22%   47.19%   -0.03%     
==========================================
  Files         116      116              
  Lines        9218     9229      +11     
==========================================
+ Hits         4353     4356       +3     
- Misses       4865     4873       +8     

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