refactor: V2 "mouseable" canvas objects, remove mouse logic from qt/jupyter views

[tlambert03]

this pulls the logic that was patching mouse events from the Qt/Jupyter view side of things, and patches them directly on the canvases themselves. The canvas becomes a "Mouseable" object, and gains mouseMoved, mousePressed, and mouseReleased signals, as well as on_mouse_x() callbacks. This paves the way for some of the stuff in histograms to use the same base logic as the image canvas, without needing to deal with them each separately on the "main" view objects.

it also fixes pygfx again to work for jupyter, and gives a more generic run_app() method (which will help for #62 )

[codecov]

Codecov Report

Attention: Patch coverage is 64.40678% with 84 lines in your changes missing coverage. Please review.

Please upload report for BASE (v2-mvc@7dba289). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/ndv/views/_app.py	62.00%	38 Missing ⚠️
src/ndv/views/_mouse_events.py	40.32%	37 Missing ⚠️
src/ndv/views/_pygfx/_pygfx.py	80.64%	6 Missing ⚠️
src/ndv/views/protocols.py	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             v2-mvc      #64   +/-   ##
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  Coverage          ?   74.25%           
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  Files             ?       31           
  Lines             ?     3026           
  Branches          ?        0           
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  Hits              ?     2247           
  Misses            ?      779           
  Partials          ?        0           

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