Optimize M2 update loop: skip static doodads, incremental spatial index

- Split M2 instances into fast-path index lists (animated, particle-only,
  particle-all, smoke) to avoid iterating all 46K instances per frame
- Cache model flags (hasAnimation, disableAnimation, isSmoke, etc.) on
  M2Instance struct to eliminate per-frame hash lookups
- Replace full rebuildSpatialIndex on position/transform updates with
  incremental grid cell remove+add, preventing 8.5ms/frame rebuild cost
- Advance animTime for all instances (texture UV animation) but only
  compute bones and particles for the ~3K that need it

M2_UPDATE: 10.7ms → 2.0ms, FPS: 35 → 55-59

src/rendering/renderer.cpp

@@ -3346,7 +3346,6 @@ void Renderer::renderWorld(game::World* world, game::GameHandler* gameHandler) {
 
     auto renderEnd = std::chrono::steady_clock::now();
     lastRenderMs = std::chrono::duration<double, std::milli>(renderEnd - renderStart).count();
-
 }
 
 // initPostProcess(), resizePostProcess(), shutdownPostProcess() removed —