Differences from v1.2.0:
- Input validation (com_positions, rmsd, radius_of_gyration finiteness)
- _compute_rho_T: scalar covariance guard (ported from lambda_structures_core.py)
- _compute_sigma_s: NaN guard on correlation matrix
- _compute_lambda_F: post-computation finiteness check (warning)
- _print_statistics: NaN/Inf prominently flagged
API, return-value keys, and array shapes are UNCHANGED.