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

@@ -144,11 +144,6 @@ bool DataStore::initialize()
             success = false;
             break;
         }
-        if (!SharedMemory::createOrOpenMapping(m_payments))
-        {
-            success = false;
-            break;
-        }
         if (!SharedMemory::createOrOpenMapping(m_serviceManagementObservers))
         {
             success = false;
@@ -193,7 +188,6 @@ void DataStore::shutdown()
     SharedMemory::closeMapping(m_serviceBookings);
     SharedMemory::closeMapping(m_jobCards);
     SharedMemory::closeMapping(m_invoices);
-    SharedMemory::closeMapping(m_payments);
     SharedMemory::closeMapping(m_serviceManagementObservers);
     SharedMemory::closeMapping(m_paymentManagementObservers);
     SharedMemory::closeMapping(m_inventoryManagementObservers);
@@ -565,32 +559,6 @@ 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