fixed gene sprites not loading

[Mel-Raeven]

This pull request refactors the src/sprite_manager.py file to improve code clarity and type safety, particularly regarding dragon sprite retrieval and color constants. The main changes involve moving color constant imports to the module level, improving function signatures with Optional typing, and ensuring that stage values are always handled as strings.

Improvements to imports and code organization:

• Moved dragon color constant imports (DRAGON_RED, DRAGON_BLUE, etc.) from inside methods to the top of the file, reducing redundancy and improving import clarity. [1] [2] [3]

Type safety and function signature improvements:

• Updated function arguments and internal variables to use Optional typing for stage, dragon_type, and enchantments, making the code more robust and type-safe. [1] [2]
• Ensured that stage is always treated as a string within get_dragon_sprite, reducing the risk of type errors.

Bug fixes and fallback improvements:

• Changed fallback sprite creation to use _create_pixel_art_sprite instead of the deprecated _create_placeholder_sprite.
• Fixed fallback logic in get_dragon_with_enchantments to always use the dragon's current stage, ensuring correct sprite selection.

Minor interface changes:

• Changed the return type of _load_sprite_from_file to Optional[pygame.Surface] to better reflect cases where loading may fail.
• Updated calls to get_sprite to use the new actual_stage variable, ensuring consistent stage handling.