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

include/pipeline/dbc_loader.hpp

@@ -3,6 +3,7 @@
 #include <vector>
 #include <map>
 #include <string>
+#include <string_view>
 #include <cstdint>
 #include <memory>
 
@@ -92,6 +93,11 @@ public:
      */
     std::string getString(uint32_t recordIndex, uint32_t fieldIndex) const;
 
+    /**
+     * Get a string field as a view (no allocation; valid while this DBCFile lives)
+     */
+    std::string_view getStringView(uint32_t recordIndex, uint32_t fieldIndex) const;
+
     /**
      * Get string by offset in string block
      * @param offset Offset into string block
@@ -99,6 +105,11 @@ public:
      */
     std::string getStringByOffset(uint32_t offset) const;
 
+    /**
+     * Get string by offset as a view (no allocation; valid while this DBCFile lives)
+     */
+    std::string_view getStringViewByOffset(uint32_t offset) const;
+
     /**
      * Find a record by ID (assumes first field is ID)
      * @param id Record ID to find