Use codecov v4, single upload step, and non-codecov reports

[Czaki]

This PR solves #13 (comment) and moves coverage upload to a separate step to make the CI logs cleaner.

It also adds support for GHA-only coverage reports using the method from
hynek.me/articles/ditch-codecov-python

[jni]

Nice! Thanks @Czaki! However it is currently failing in a weird way. 😅

[Czaki]

Nice! Thanks @Czaki! However it is currently failing in a weird way. 😅

It is not verid. I hit this every time I migrate to this schema. it is only problem with paths between operating systems...

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 75.27%. Comparing base (ff1b148) to head (3c4606b).

Files	Patch %	Lines
src/napari_graph/base_graph.py	0.00%	1 Missing ⚠️
src/napari_graph/directed_graph.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
- Coverage   80.40%   75.27%   -5.13%     
==========================================
  Files           6        6              
  Lines         546      546              
  Branches       95      121      +26     
==========================================
- Hits          439      411      -28     
  Misses         73       73              
- Partials       34       62      +28     

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[Czaki]

@jni it is ready to review.
Also contains hynek.me/articles/ditch-codecov-python

It looks like branch coverage is handled differently on codecov.io and normal report.

[jni]

Amazing! Thank you @Czaki!