3.2.1

• Add per_site, per_charge and return_annealing_values options to FermiSolver methods, for more flexible output formatting.
• Add fixed_elements option to optimise() and scan_chemical_potential_grid()
• Add plot_chempot_heatmap method to DefectThermodynamics, for convenience.
• Add include_unique_wyckoffs option to get_interstitial_sites (see #140)
• Avoid interstitial duplication in mixed-valence systems.
• Fixes and extensions for py-sc-fermi FermiSolver backend: degeneracy handling, delta_gap handling, and multiplicity scaling with non-primitive DOS cells.
• Numerical stability improvements: extend brentq Fermi level search limits, cap defect concentration bounds, and custom ConvexHull code for chemical potential spaces.
• Handle magnetization parsing for cases with N_spin_down > N_spin_up.
• Update symmetry_preference to relative symm_pref_dist_factor for more consistent behaviour across systems.
• Update interstitial clustering method to centroid to avoid over-daisy-chaining.
• Default to most common elemental oxidation states when guessing fails (following SnB approach).
• Smart n_points estimation for ChemicalPotentialGrid.get_grid().
• Update spglib error handling for compatibility with >=2.7.
• Make pydefect a softer dependency, minimising imports.
• Modularise DefectsGenerator internals for future extensibility (i.e. complexes...).
• DefectsParser refactoring and cleanup.
• Various robustness, efficiency and docs updates.