- Implement robust surface area and volume computation for polymesh_t
- Support arbitrary polygonal faces (triangles, quads, etc.) via fan triangulation
- Add vector math utilities: cross, dot, norm, and signed volume
- Validate algorithm correctness using unit cube test case
- Ensure right-hand rule compliance for accurate volume sign
Test: Added test case with unit cube (8 vertices, 6 quads)
Expected: area = 6.0, volume = 1.0 → actual results match
