Add check_sdist job to validate source wheels and fix nanobind submodule contents in source wheel (recursive clone option was missing). closes #485

[slayoo]

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.92%. Comparing base (251de18) to head (5638e9b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #490   +/-   ##
=======================================
  Coverage   91.92%   91.92%           
=======================================
  Files          56       56           
  Lines        2564     2564           
  Branches      144      144           
=======================================
  Hits         2357     2357           
  Misses        132      132           
  Partials       75       75           

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