MNT build clean wheel

[MatthewSZhang]

Checklist

• Used a personal fork to propose changes
• A reference to a related issue: MNT exclude .pyx files in wheel #223
• A description of the changes:
  • Exclude .pyx files in wheels, see ref
  • Split build env from default, see discussion
  • Drop python 3.9 support to use meson-python 0.19.0 wheel.exclude section
  • Add strict lowest deps test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (c40e633) to head (6fb7c55).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #224   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          853       858    +5     
=========================================
+ Hits           853       858    +5     

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