perf: eliminate ~70 unnecessary sqrt ops per frame, optimize caches and threading

Squared distance optimizations across 30 files:
- Convert glm::length() comparisons to glm::dot() (no sqrt)
- Use glm::inversesqrt() for check-then-normalize patterns (1 rsqrt vs 2 sqrt)
- Defer sqrt to after early-out checks in collision/movement code
- Hottest paths: camera_controller (21), weather particles, WMO collision,
  transport movement, creature interpolation, nameplate culling

Container and algorithm improvements:
- std::map<string> → std::unordered_map for asset/DBC/MPQ/warden caches
- std::mutex → std::shared_mutex for asset_manager and mpq_manager caches
- std::sort → std::partial_sort in lighting_manager (top-2 of N volumes)
- Double-lookup find()+operator[] → insert_or_assign in game_handler
- Add reserve() for per-frame vectors: weather, swim_effects, WMO/M2 collision

Threading and synchronization:
- Replace 1ms busy-wait polling with condition_variable in character_renderer
- Move timestamp capture before mutex in logger
- Use memory_order_acquire/release for normal map completion signaling

API additions:
- DBC getStringView()/getStringViewByOffset() for zero-copy string access
- Parse creature display IDs from SMSG_CREATURE_QUERY_SINGLE_RESPONSE

src/rendering/lens_flare.cpp

@@ -301,10 +301,11 @@ void LensFlare::render(VkCommandBuffer cmd, const Camera& camera, const glm::vec
     // Sun billboard rendering is sky-locked (view translation removed), so anchor
     // flare projection to camera position along sun direction to avoid parallax drift.
     glm::vec3 sunDir = sunPosition;
-    if (glm::length(sunDir) < 0.0001f) {
+    float sunDirLenSq = glm::dot(sunDir, sunDir);
+    if (sunDirLenSq < 1e-8f) {
         return;
     }
-    sunDir = glm::normalize(sunDir);
+    sunDir *= glm::inversesqrt(sunDirLenSq);
     glm::vec3 anchoredSunPos = camera.getPosition() + sunDir * 800.0f;
 
     // Calculate sun visibility