Code currently mixes British and American spellings for centre / center

[bjmorgan]

Problem

The codebase currently has inconsistent spelling between British "centre" and American "center", creating confusion for users and inconsistency in the API.

British spelling currently used:

• Site.centre property (core base class)
• DynamicVoronoiSite._centre_coords, .calculate_centre()
• Builder methods: with_spherical_sites(centres=...), with_polyhedral_sites(centre_species=...)
• Internal tools: get_coordination_indices(centre_species=...)

American spelling currently used:

• ReferenceBasedSites.create_polyhedral_sites(center_species=...) (public, released)
• ReferenceBasedSites.create_dynamic_voronoi_sites(center_species=...)
• Recently updated: PolyhedralSite(reference_center=...), DynamicVoronoiSite(reference_center=...)

Arguments for Standardising on American Spelling

1. Ecosystem consistency: PyMatGen (our primary dependency) uses American spelling throughout its API
2. Python ecosystem standard: NumPy, SciPy, Matplotlib, and virtually all scientific Python libraries use "center"
3. International accessibility: American spelling is more familiar to the global Python developer community
4. Future-proofing: New users will expect American spelling based on ecosystem conventions
5. Minimal breaking changes: The analysis below shows limited public API impact

Breaking Change Analysis

Public API breaking changes:

• Builder methods: centre_species → center_species, centres → centers
  • Impact: LOW - Builder API is relatively new with limited adoption

Non-breaking changes (using aliases):

• Site.centre → add Site.center alias, keep centre with deprecation warning
  • Impact: NONE - existing code continues to work

Internal changes (no user impact):

• get_coordination_indices(centre_species=...) → center_species (not intended as public API)
• Internal methods and attributes

Proposed Solution

Core Properties

• Add Site.center property as alias to Site.centre
• Add deprecation warning to Site.centre
• Update DynamicVoronoiSite methods: calculate_centre() → calculate_center(), _centre_coords → _center_coords

Builder API

• Update builder method parameters: centre_species → center_species, centres → centers
• Update factory function parameters to match

Internal Tools

• Update get_coordination_indices(centre_species=...) → center_species
• Update other internal utilities

Documentation

• Search and replace "centre" → "center" in all docstrings, comments, and documentation
• Update examples to use American spelling
• Document breaking changes in release notes

Benefits

• Consistency: Single spelling convention throughout the API
• Developer experience: Matches expectations from other Python scientific libraries
• Maintainability: Reduces cognitive load when developing and reviewing code
• Ecosystem integration: Better alignment with PyMatGen and broader Python ecosystem