Add pyproject validation

[blink1073]

Use https://github.com/abravalheri/validate-pyproject to validate the pyproject.toml, including trove classifiers.

[codecov-commenter]

Codecov Report

Base: 72.57% // Head: 72.51% // Decreases project coverage by -0.06% ⚠️

Coverage data is based on head (62bee8c) compared to base (bf26b59).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1020      +/-   ##
==========================================
- Coverage   72.57%   72.51%   -0.07%     
==========================================
  Files          64       64              
  Lines        8251     8251              
  Branches     1257     1257              
==========================================
- Hits         5988     5983       -5     
- Misses       1848     1852       +4     
- Partials      415      416       +1     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/handlers.py	57.79% <0.00%> (-1.04%)	⬇️

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