Refactor ROM handling and remove SharedRom singleton for improved architecture

- Eliminated the SharedRom class to enhance modularity and reduce global state management.
- Updated various classes to directly manage ROM instances, improving clarity and encapsulation.
- Added new functions for loading messages and colors from ROM, enhancing functionality.
- Refactored Canvas and Editor classes to utilize direct ROM references, streamlining interactions.
- Improved documentation and comments for better code understanding and maintainability.

src/app/rom.cc

@@ -649,6 +649,4 @@ absl::Status Rom::WriteColor(uint32_t address, const gfx::SnesColor &color) {
   return WriteShort(address, bgr);
 }
 
-std::shared_ptr<Rom> SharedRom::shared_rom_ = nullptr;
-
 }  // namespace yaze