bsym v2.2.0

Bug fixes, correctness improvements, and performance optimisations.

Bug Fixes

Mutable default argument in SymmetryGroup.__init__: all instances shared the same list, risking cross-contamination between groups.
Stale caches after extend()/append(): unique_index_mappings and stacked_index_mappings are now invalidated when operations are added.
Infinite loop risk in random_unique_configurations: added a max_attempts parameter (default 1000) with RuntimeError when the configuration space appears exhausted.
Uniform sampling failure counter: rejection by the acceptance test no longer counts as a failure to find a novel configuration, preventing spurious RuntimeError for highly degenerate configurations.
Wrong class_str in SpaceGroup: was 'SymmetryGroup' instead of 'SpaceGroup'.
bsym.bsym called sys.exit() on import; replaced with raise ImportError(...).
SymmetryGroup.__mul__ lost subclass type: SpaceGroup * SpaceGroup returned a plain SymmetryGroup; now preserves the left operand's type.

Matrix transpose for permutation inversion instead of np.linalg.inv.
np.argmax for index_mapping and as_vector instead of Python loops.
Set-based deduplication of symmetry operation vectors in the pymatgen interface.
Vectorised apply_species_mapping using numpy fancy indexing.
End-to-end: 3.9x speedup on ternary composition enumeration, 2.4x on random sampling.

Fixed type annotations for cache fields and labels property in SymmetryGroup.
Updated SymmetryOperation.__init__ docstring to document deprecated np.matrix acceptance.
Removed outdated docstrings referencing numpy.matrix subclassing.
Removed unused imports and duplicate permutation_as_config_number function.
Simplified SymmetryOperation.__init__ type checking.
Replaced deprecated tqdm_notebook with tqdm.auto.

permutation_as_config_number (module-level function in configuration_space) has been removed.
Importing bsym.bsym now raises ImportError instead of calling sys.exit().