epic: refactor SDL2_Renderer usage to IRenderer and queued texture rendering

- Updated the testing guide to clarify the testing framework's organization and execution methods, improving user understanding.
- Refactored CMakeLists to include new platform-specific files, ensuring proper integration of the rendering backend.
- Modified main application files to utilize the new IRenderer interface, enhancing flexibility in rendering operations.
- Implemented deferred texture management in various components, allowing for more efficient graphics handling and improved performance.
- Introduced new methods for texture creation and updates, streamlining the rendering process across the application.
- Enhanced logging and error handling in the rendering pipeline to facilitate better debugging and diagnostics.

src/app/rom.cc

@@ -105,10 +105,8 @@ absl::StatusOr<std::array<gfx::Bitmap, kNumLinkSheets>> LoadLinkGraphics(
     link_graphics[i].Create(gfx::kTilesheetWidth, gfx::kTilesheetHeight,
                             gfx::kTilesheetDepth, link_sheet_8bpp);
     link_graphics[i].SetPalette(rom.palette_group().armors[0]);
-    // TODO: Renderer refactor to use IRenderer or defer for later when GraphicsEditor is opened.
-    // if (SDL_Renderer *renderer = Renderer::Get().renderer(); renderer != nullptr) {
-    //   Renderer::Get().RenderBitmap(&link_graphics[i]);
-    // }
+    // Texture creation is deferred until GraphicsEditor is opened and renderer is available.
+    // The graphics will be queued for texturing when needed via Arena's deferred system.
   }
   return link_graphics;
 }