[Copilot]

The failing Testing (3.10) GitHub Actions job was caused by a Ruff SIM108 violation in the weighted Kabsch path, not a Python 3.10 compatibility issue. This updates that code path to satisfy CI linting while preserving behavior.

• CI failure root cause

  • Replace the if/else assignment for default weights in kabsch_weighted with the equivalent inline expression Ruff expects.

• Behavior guard

  • Add a focused regression test covering the W=None path against explicit uniform weights to keep the default weighted behavior pinned.

• Illustrative change

  W = np.ones(len(P)) / len(P) if W is None else W