Reduce runtime streaming stutter by throttling heavy spawn workloads

- Add per-frame cap for first-time creature model loads to spread expensive model/texture decode work across frames instead of burst loading.

- Keep cached creature spawns flowing while deferring uncached display IDs, preserving world population updates with smoother frame pacing.

- Defer transport WMO doodad instancing into a queued batch processor with a strict per-frame budget to avoid multi-hundred-ms spikes when ships/elevators register.

- Process deferred transport doodad batches in both normal gameplay update and loading-screen warmup loop so heavy transport setup can be amortized before and after world entry.

- Cleanup pending transport doodad batches on gameobject despawn to prevent stale work and avoid attaching children to removed parents.

- Lower character texture cache miss logging from INFO to DEBUG to reduce log I/O contention during movement-heavy asset streaming.

src/rendering/character_renderer.cpp

@@ -440,7 +440,7 @@ GLuint CharacterRenderer::loadTexture(const std::string& path) {
             textureCacheBytes_ / (1024 * 1024), " MB > ",
             textureCacheBudgetBytes_ / (1024 * 1024), " MB (textures=", textureCache.size(), ")");
     }
-    core::Logger::getInstance().info("Loaded character texture: ", path, " (", blpImage.width, "x", blpImage.height, ")");
+    core::Logger::getInstance().debug("Loaded character texture: ", path, " (", blpImage.width, "x", blpImage.height, ")");
     return texId;
 }