Add runtime API support for updating characterGO and related offsets in CharacterEntity.cs

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This PR adds runtime API support for dynamically updating character properties that were previously only modifiable during initialization. The CharacterEntity class now exposes public methods to update characterGO, characterObjectOffset, characterObjectRotation, and characterLabelOffset at runtime.

Problem

Previously, these critical character properties could only be set during entity initialization via the Initialize() method, making dynamic character management difficult:

// Before: Only possible during initialization
character.Initialize(id, prefab, offset, rotation, labelOffset);

// Runtime updates were impossible - properties had private setters
// character.characterObjectOffset = newOffset; // ❌ Compilation error

Solution

Added five new public methods to enable runtime updates:

// New runtime APIs
bool SetCharacterGO(GameObject newCharacterGO, bool synchronize = true);
GameObject GetCharacterGO();
bool SetCharacterObjectOffset(Vector3 newOffset, bool synchronize = true);
bool SetCharacterObjectRotation(Quaternion newRotation, bool synchronize = true);
bool SetCharacterLabelOffset(Vector3 newOffset, bool synchronize = true);

Usage Examples

Dynamic character model switching:

GameObject newModel = Resources.Load<GameObject>("AlternativeCharacter");
character.SetCharacterGO(newModel);

Runtime position adjustments:

// Adjust character height dynamically
character.SetCharacterObjectOffset(new Vector3(0, 1.5f, 0));

// Rotate character to face a target
character.SetCharacterObjectRotation(Quaternion.LookRotation(targetDirection));

// Move label based on character state
character.SetCharacterLabelOffset(new Vector3(0, isJumping ? 3f : 2f, 0));

Implementation Details

• Full GameObject replacement: SetCharacterGO() handles mesh updates, bounds recalculation, and cleanup
• Live transform updates: Position and rotation changes immediately apply to GameObjects
• Label positioning: Automatically finds and updates TextMeshProUGUI components
• Error handling: Proper validation with meaningful error messages
• Synchronization ready: Optional sync parameter for future multiplayer support
• Backward compatibility: All existing code continues to work unchanged

Testing & Documentation

• Comprehensive test suite covering all APIs and edge cases
• Interactive demonstration script for runtime testing
• Complete API documentation with usage examples
• Validation of backward compatibility with existing tests

This enables dynamic character customization, procedural generation, animation-driven updates, and improved testing workflows while maintaining full backward compatibility.

Fixes #28.

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