Pin casadi below 3.8 for pip installs

[ASP-SuperExplorer]

Fixes #2082.

A fresh pip/uv install can currently resolve to casadi 3.8.0 with nlopt 2.11.0. That pair has been reported to crash on Windows during interpreter shutdown, which shows up as 0xC0000005 or heap corruption even when the CadQuery script itself completed.

This pins the pip dependency to casadi<3.8, so new installs stay on the last known-good 3.7.x line. I also added a small metadata test so the constraint does not get dropped accidentally.

Tested locally:

python -m pytest tests/test_package_metadata.py -q
python - <<'PY'
import cadquery as cq
result = cq.Workplane('XY').box(10, 20, 5)
print(result.val().ShapeType(), result.val().isValid(), result.val().Volume())
PY

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.67%. Comparing base (a6bedc0) to head (f6f3f02).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2095   +/-   ##
=======================================
  Coverage   95.67%   95.67%           
=======================================
  Files          30       30           
  Lines        9534     9534           
  Branches     1421     1421           
=======================================
  Hits         9122     9122           
  Misses        255      255           
  Partials      157      157           

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