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/weather.cpp

@@ -221,6 +221,7 @@ void Weather::update(const Camera& camera, float deltaTime) {
 
     // Update position buffer
     particlePositions.clear();
+    particlePositions.reserve(particles.size());
     for (const auto& particle : particles) {
         particlePositions.push_back(particle.position);
     }
@@ -232,9 +233,10 @@ void Weather::updateParticle(Particle& particle, const Camera& camera, float del
 
     // Reset if lifetime exceeded or too far from camera
     glm::vec3 cameraPos = camera.getPosition();
-    float distance = glm::length(particle.position - cameraPos);
+    glm::vec3 toCamera = particle.position - cameraPos;
+    float distSq = glm::dot(toCamera, toCamera);
 
-    if (particle.lifetime >= particle.maxLifetime || distance > SPAWN_VOLUME_SIZE ||
+    if (particle.lifetime >= particle.maxLifetime || distSq > SPAWN_VOLUME_SIZE * SPAWN_VOLUME_SIZE ||
         particle.position.y < cameraPos.y - 20.0f) {
         // Respawn at top
         particle.position = getRandomPosition(cameraPos);