Refactor the handling of graphics sheets by introducing a singleton class `GraphicsSheetManager`. This centralizes the management of graphics sheets, replacing direct access through the `Rom` object. Key changes include:
- Updated various methods across multiple classes to use `GraphicsSheetManager::GetInstance()` for accessing and manipulating graphics sheets.
- Introduced standalone functions `LoadLinkGraphics`, `LoadAllGraphicsData`, and `SaveAllGraphicsData` for loading and saving graphics data.
- Refactored the `Rom` class to remove methods and member variables related to graphics sheet management.
- Updated `OverworldEditor` to use `std::array` for `maps_bmp_` and added error handling for `std::bad_alloc` exceptions.
- Improved code modularity and error handling throughout the application.
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