v0.1.4 — Exact subgroup predicates and Python 3.14 support

Adds exact integer-subgroup queries to the SNF decomposition API:

• SNFDecomposition.contains(...) for exact lattice-subgroup membership;
• SNFDecomposition.same_subgroup(...) for equality of embedded integer subgroups;
• stricter integer-vector validation and exact handling of NumPy integer inputs;
• PeriodicComponent.same_fragment(...) now delegates subgroup membership to the SNF decomposition, with matching robustness improvements for instance keys.

The new subgroup API supports downstream symmetry-aware periodic-graph workflows while remaining general-purpose within pbcgraph.

Also included:

• Python 3.14 in the tested support matrix;
• refreshed GitHub Actions dependencies;
• expanded tests and API/theory documentation.