Add shared basis conversion to motionCore

[snkmcb]

Summary

• Add signed-permutation basis conversion primitives to motionCore, covering positions and rotations with validation.
• Have motionSource reuse the shared conversion while preserving its public CanonicalBasis type.
• Update package manifests, documentation, and changelog for the unreleased 0.5.2 version.

Verification

• Passed motionCore_basis, motionCore_boundaries, motionSource_conversion, and motionSource_boundaries.
• Passed scripts/check_docs.py.
• Built and ran a clean CMake consumer against the locally installed 0.5.2 motionCore package.

Follow-up

• Publish motionCore 0.5.2 and update its pinned package digest before migrating motion-connectors to this new API.