feat: add basic profiling/metrics system (#104)

- Add ProfilingMetrics struct to track performance data
- Track frame time (current and 60-frame rolling average)
- Calculate FPS from average frame time
- Count draw calls, UI elements, and visible elements per frame
- Track total runtime and current frame number
- PyScene counts elements during render
- Expose metrics via mcrfpy.getMetrics() returning dict

This provides basic performance monitoring capabilities for
identifying bottlenecks and optimizing rendering performance.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/PyScene.cpp

@@ -72,8 +72,16 @@ void PyScene::render()
     // Render in sorted order (no need to copy anymore)
     for (auto e: *ui_elements)
     {
-        if (e)
+        if (e) {
+            // Track metrics
+            game->metrics.uiElements++;
+            if (e->visible) {
+                game->metrics.visibleElements++;
+                // Count this as a draw call (each visible element = 1+ draw calls)
+                game->metrics.drawCalls++;
+            }
             e->render();
+        }
     }
     
     // Display is handled by GameEngine