Clean up legacy code

- Remove FileManager and related file-based persistence logic
- Remove obsolete observer persistence utilities
- Remove unused service APIs and includes
- Delete duplicate DataStore mutex stubs
- Perform general dead-code cleanup

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/datastores/DataStore.cpp

@@ -565,32 +565,6 @@ void DataStore::saveInventoryManagementObservers(util::Map<std::string, User*>&
     saveObservers(m_inventoryManagementObservers, observers);
 }
 
-/*
-Function: lockDataStore
-Description: Acquires exclusive access to the datastore.
-Parameters:
-    - None
-Returns:
-    - bool: True if the datastore was successfully locked, otherwise false
-*/
-bool DataStore::lockDataStore()
-{
-    return false;
-}
-
-/*
-Function: unlockDataStore
-Description: Releases exclusive access to the datastore.
-Parameters:
-    - None
-Returns:
-    - bool: True if the datastore was successfully unlocked, otherwise false
-*/
-bool DataStore::unlockDataStore()
-{
-    return false;
-}
-
 /*
 Function: lockDataStore
 Description: Acquires the datastore mutex, providing