BTHLABS-61: Service layer refactoring

A journey to fix `ValidationError` in Pocket imports turned service
layer refactoring :D

services/backend/testing/hotpocket_backend_testing/fixtures/saves/association.py

@@ -76,6 +76,18 @@ def starred_association_out(starred_association):
     )
 
 
+@pytest.fixture
+def deleted_save_association(association_factory, deleted_save):
+    return association_factory(target=deleted_save)
+
+
+@pytest.fixture
+def deleted_save_association_out(deleted_save_association):
+    return AssociationWithTargetOut.model_validate(
+        deleted_save_association, from_attributes=True,
+    )
+
+
 @pytest.fixture
 def other_account_association(association_factory, other_account):
     return association_factory(account=other_account)
@@ -124,6 +136,18 @@ def other_account_starred_association_out(other_account_starred_association):
     )
 
 
+@pytest.fixture
+def other_account_deleted_save_association(association_factory, other_account, deleted_save):
+    return association_factory(account=other_account, target=deleted_save)
+
+
+@pytest.fixture
+def other_account_deleted_save_association_out(other_account_deleted_save_association):
+    return AssociationWithTargetOut.model_validate(
+        other_account_deleted_save_association, from_attributes=True,
+    )
+
+
 @pytest.fixture
 def browsable_associations(association,
                            deleted_association,