render: add OpenGL resource caching; optimize texture handling

Mildly improves rendering performance by caching OpenGL resources.
Namely:

- Cache shader program, VBO/EBO, and textures per output
- Automatically free image data after GPU upload
- Force RGBA format for consistent texture handling
- Track texture state across output changes
- Add texture invalidation on image changes

This reduces the memory usage by a solid 30MB, but it's still not quite
enough. I expect (or rather, hope) that we can cut it by half.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I6a6a6964eebc783c5bc07b1fef7548a8d49f529c

include/chroma.h

@@ -62,6 +62,14 @@ typedef struct {
 
   // Associated wallpaper
   chroma_image_t *image;
+
+  // OpenGL resource cache
+  GLuint texture_id;
+  GLuint shader_program;
+  GLuint vbo;
+  GLuint ebo;
+  bool gl_resources_initialized;
+  bool texture_uploaded;
 } chroma_output_t;
 
 // Config mapping structure
@@ -150,6 +158,7 @@ void chroma_egl_cleanup(chroma_state_t *state);
 int chroma_surface_create(chroma_state_t *state, chroma_output_t *output);
 void chroma_surface_destroy(chroma_output_t *output);
 int chroma_render_wallpaper(chroma_state_t *state, chroma_output_t *output);
+void chroma_output_invalidate_texture(chroma_output_t *output);
 
 // Layer shell functions
 void chroma_layer_surface_configure(void *data,
@@ -219,4 +228,4 @@ extern const struct zwlr_layer_surface_v1_listener
 // Global state for signal handling
 extern volatile sig_atomic_t chroma_should_quit;
 
-#endif // CHROMA_H
+#endif // CHROMA_H