Add BackgroundBuffer class for managing SNES background graphics

Introduce the BackgroundBuffer class to handle tile management and rendering for SNES backgrounds. This includes methods for setting and getting tile values, clearing the buffer, and drawing tiles and backgrounds using provided graphics data. The class is designed to facilitate efficient graphics rendering in the application.

src/app/gfx/gfx.cmake

@@ -1,10 +1,13 @@
 set(
   YAZE_APP_GFX_SRC
+  app/gfx/arena.cc
+  app/gfx/background_buffer.cc
   app/gfx/bitmap.cc
   app/gfx/compression.cc
   app/gfx/scad_format.cc
   app/gfx/snes_palette.cc
   app/gfx/snes_tile.cc
   app/gfx/snes_color.cc
+  app/gfx/tilemap.cc
   app/gfx/tilesheet.cc
 )