Refactor graphics sheet management with singleton class

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.

src/app/editor/dungeon/dungeon_editor.cc

@@ -109,7 +109,7 @@ absl::Status DungeonEditor::Initialize() {
   ASSIGN_OR_RETURN(current_palette_group_,
                    gfx::CreatePaletteGroupFromLargePalette(full_palette_));
 
-  graphics_bin_ = rom()->gfx_sheets();
+	graphics_bin_ = GraphicsSheetManager::GetInstance().gfx_sheets();
   // Create a vector of pointers to the current block bitmaps
   for (int block : rooms_[current_room_id_].blocks()) {
     room_gfx_sheets_.emplace_back(&graphics_bin_[block]);