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/sky_system.cpp

@@ -156,8 +156,9 @@ void SkySystem::render(VkCommandBuffer cmd, VkDescriptorSet perFrameSet,
 }
 
 glm::vec3 SkySystem::getSunPosition(const SkyParams& params) const {
-    glm::vec3 dir = glm::normalize(params.directionalDir);
-    if (glm::length(dir) < 0.0001f) {
+    float dirLenSq = glm::dot(params.directionalDir, params.directionalDir);
+    glm::vec3 dir = (dirLenSq > 1e-8f) ? params.directionalDir * glm::inversesqrt(dirLenSq) : glm::vec3(0.0f);
+    if (dirLenSq < 1e-8f) {
         dir = glm::vec3(0.0f, 0.0f, -1.0f);
     }
     glm::vec3 sunDir = -dir;