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[bot]]

Codecov Report

Attention: Patch coverage is 22.22222% with 21 lines in your changes missing coverage. Please review.

Project coverage is 47.34%. Comparing base (2815bad) to head (ba30f2d).

Files with missing lines	Patch %	Lines
lib/pages/editor/editor.dart	23.52%	13 Missing :warning:
lib/components/canvas/canvas_gesture_detector.dart	20.00%	8 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1355 +/- ## ========================================== - Coverage 47.39% 47.34% -0.05% ========================================== Files 114 114 Lines 8959 8976 +17 ========================================== + Hits 4246 4250 +4 - Misses 4713 4726 +13 ```

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[adil192]

This looks good from the code. What device/s have you tested with? iirc pressing the S-pen button while hovering made the stylus not work temporarily

[3akev]

This looks good from the code. What device/s have you tested with? iirc pressing the S-pen button while hovering made the stylus not work temporarily

I tested this on a Galaxy S6 Lite with the S-pen. Unfortunately I don't have access to another device with a stylus, so I can't test this further. It should work on other devices, though.