Address review feedback on PR #68012

Fix the CI failures and review comments from PR #68012:
- Remove the dead module-level VersionBundle construction in
  schema/versions/__init__.py that referenced names only imported
  under TYPE_CHECKING, breaking the lazy cadwyn import on any access
  to the module and causing NameError in ~30 task-sdk tests.
- Remove a duplicated old_ver_client fixture and import block that
  had been pasted into test_task_instances.py, which triggered
  mypy no-redef and ruff F811/E402 failures in Static checks.
- Use func.min(start_date) instead of ordering by TaskReschedule.id
  when computing the first reschedule start date, since insertion
  order does not guarantee chronological order.

Author: hkc-8010

airflow-core/src/airflow/api_fastapi/execution_api/routes/task_instances.py

@@ -299,10 +299,7 @@ def ti_run(
         first_task_reschedule_start_date = None
         if task_reschedule_count > 0:
             first_task_reschedule_start_date = session.scalar(
-                select(TaskReschedule.start_date)
-                .where(TaskReschedule.ti_id == task_instance_id)
-                .order_by(TaskReschedule.id.asc())
-                .limit(1)
+                select(func.min(TaskReschedule.start_date)).where(TaskReschedule.ti_id == task_instance_id)
             )
 
         dr.team_name = get_team_name_for_ti(task_instance_id, session)