[fix] resolve 16 mypy errors across 9 test files (make quality gate)

type-clean the test files so make quality (mypy roboco/ tests/) is green:
- Any-typed locals for the two TypeError-asserting scoping tests (bypass
  the required-arg check without getattr/ruff B009)
- Any-typed view for the shutdown-drain _drain_bg_tasks override (bypass
  mypy method-assign without setattr/ruff B010)
- cast("uuid.UUID", ...) / cast("UUID", ...) for SQLAlchemy UUID[Any]
  returns (TC006-quoted), config=None for AgentInstance stubs, None-narrowed
  await_args, Iterator return on a yielding fixture, UUID annotation on the
  _task helper. No type:ignore / noqa.

tests/integration/services/test_active_task_owns_branch_scoping.py

@@ -71,7 +71,7 @@ async def _seed_project(db: AsyncSession, slug: str) -> ProjectTable:
     return project
 
 
-def _task(project_id, *, branch: str, status: TaskStatus) -> TaskTable:
+def _task(project_id: UUID, *, branch: str, status: TaskStatus) -> TaskTable:
     return TaskTable(
         id=uuid4(),
         title=f"task {branch}",
@@ -102,8 +102,10 @@ async def test_branch_owned_only_by_its_own_project(db_session: AsyncSession) ->
     proj_b = await _seed_project(db_session, "gca-collide-b")
     db_session.add_all(
         [
-            _task(proj_a.id, branch=_BRANCH, status=TaskStatus.IN_PROGRESS),
-            _task(proj_b.id, branch=_BRANCH, status=TaskStatus.COMPLETED),
+            _task(
+                cast("UUID", proj_a.id), branch=_BRANCH, status=TaskStatus.IN_PROGRESS
+            ),
+            _task(cast("UUID", proj_b.id), branch=_BRANCH, status=TaskStatus.COMPLETED),
         ]
     )
     await db_session.flush()