Armature: optimization + javadoc

[capdevon]

This PR refactors the Armature class to enhance clarity, maintainability, and reliability. Key changes include:

• Improved and expanded Javadoc documentation for public methods and class members.
• Renamed skinningMatrixes to skinningMatrices for correct and consistent naming.
• Replaced wildcard and unused imports with explicit imports for better readability.
• Enhanced type safety and code clarity in serialization/deserialization logic.
• Updated copyright year.

These changes are non-breaking and aimed at improving code quality and maintainability.