build: use uv for project management

[tlambert03]

out with the old, in with the new. ❤️ uv

[codecov]

Codecov Report

Attention: Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.74%. Comparing base (1084189) to head (0ccbfd1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/magicgui/widgets/_function_gui.py	0.00%	1 Missing ⚠️
src/magicgui/widgets/bases/_categorical_widget.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #700      +/-   ##
==========================================
- Coverage   88.85%   88.74%   -0.11%     
==========================================
  Files          40       40              
  Lines        4809     4807       -2     
==========================================
- Hits         4273     4266       -7     
- Misses        536      541       +5     

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[tlambert03]

@brisvag @Czaki ... what was the fix for the conftest thing in the new napari tests?

ImportError while loading conftest '/home/runner/work/magicgui/magicgui/napari/napari/src/napari/conftest.py'.
_pytest.pathlib.ImportPathMismatchError: ('napari.conftest', '/opt/hostedtoolcache/Python/3.10.17/x64/lib/python3.10/site-packages/napari/conftest.py', PosixPath('/home/runner/work/magicgui/magicgui/napari/napari/src/napari/conftest.py'))