feat: downsample oversized textures

[tlambert03]

fixes #259 for both vispy and pygfx. If the requested data is larger than the GPU allows, we downsample with a strided view.

[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.76%. Comparing base (7b56e80) to head (ec8bb85).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ndv/views/_pygfx/_array_canvas.py	88.00%	3 Missing ⚠️
src/ndv/views/_vispy/_array_canvas.py	84.61%	2 Missing ⚠️
src/ndv/views/_vispy/_util.py	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #260      +/-   ##
==========================================
+ Coverage   86.65%   86.76%   +0.11%     
==========================================
  Files          48       50       +2     
  Lines        5687     5742      +55     
==========================================
+ Hits         4928     4982      +54     
- Misses        759      760       +1     

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