perf: improve perf in SIP-68 migration (#19416)

* chore: improve perf in SIP-68 migration

* Small fixes

* Create tables referenced in SQL

* Update logic in SqlaTable as well

* Fix unit tests

scripts/benchmark_migration.py

@@ -102,7 +102,10 @@ def find_models(module: ModuleType) -> List[Type[Model]]:
     while tables:
         table = tables.pop()
         seen.add(table)
-        model = getattr(Base.classes, table)
+        try:
+            model = getattr(Base.classes, table)
+        except AttributeError:
+            continue
         model.__tablename__ = table
         models.append(model)