Refactor Renderer access and enhance graphics loading functionality

- Replaced instances of Renderer::GetInstance() with Renderer::Get() for consistency across the codebase.
- Updated various rendering methods to streamline bitmap updates and enhance performance.
- Removed unused includes and comments to improve code clarity and maintainability.

src/app/zelda3/screen/dungeon_map.cc

@@ -35,7 +35,7 @@ absl::Status LoadDungeonMapGfxFromBinary(Rom &rom,
                                 converted_bin.begin() + ((i + 1) * 0x1000));
         sheets[i] = gfx::Bitmap(128, 32, 8, gfx_sheets[i]);
         sheets[i].SetPalette(*rom.mutable_dungeon_palette(3));
-        core::Renderer::GetInstance().RenderBitmap(&sheets[i]);
+        core::Renderer::Get().RenderBitmap(&sheets[i]);
       }
     } else {
       return absl::InternalError("Failed to load dungeon map tile16");

src/app/zelda3/screen/inventory.cc

@@ -69,7 +69,7 @@ absl::Status Inventory::Create() {
 
   bitmap_.Create(256, 256, 8, data_);
   bitmap_.SetPalette(palette_);
-  Renderer::GetInstance().RenderBitmap(&bitmap_);
+  Renderer::Get().RenderBitmap(&bitmap_);
   return absl::OkStatus();
 }
 
@@ -88,7 +88,7 @@ absl::Status Inventory::BuildTileset() {
   auto hud_pal_group = rom()->palette_group().hud;
   palette_ = hud_pal_group[0];
   tilesheets_bmp_.SetPalette(palette_);
-  Renderer::GetInstance().RenderBitmap(&tilesheets_bmp_);
+  Renderer::Get().RenderBitmap(&tilesheets_bmp_);
   return absl::OkStatus();
 }