Add in-memory read cache with CUD-based invalidation

backend/app/repositories/users_repo.py

@@ -57,6 +57,7 @@ class UsersRepository:
         provider_user_id: str | None = None,
     ) -> User:
         user = self.get_by_sub(user_sub)
+        changed = False
         if user is None:
             user = User(
                 user_sub=user_sub,
@@ -68,17 +69,30 @@ class UsersRepository:
                 status=status,
             )
             self.db.add(user)
+            changed = True
         else:
-            if provider_user_id is not None:
+            if provider_user_id is not None and user.provider_user_id != provider_user_id:
                 user.provider_user_id = provider_user_id
-            user.username = username
-            user.email = email
-            user.display_name = display_name
-            user.is_active = is_active
-            user.status = status
+                changed = True
+            if user.username != username:
+                user.username = username
+                changed = True
+            if user.email != email:
+                user.email = email
+                changed = True
+            if user.display_name != display_name:
+                user.display_name = display_name
+                changed = True
+            if user.is_active != is_active:
+                user.is_active = is_active
+                changed = True
+            if user.status != status:
+                user.status = status
+                changed = True
 
-        self.db.commit()
-        self.db.refresh(user)
+        if changed:
+            self.db.commit()
+            self.db.refresh(user)
         return user
 
     def update_member(