[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/unit/runtime/test_reaper_subprocess_timeout.py

@@ -280,4 +280,6 @@ async def test_check_health_skips_agent_on_inspect_timeout_not_aborts(
     assert hang.killed
     # a2 WAS reached despite a1's timeout — the sweep continued.
     handle.assert_awaited_once()
-    assert handle.await_args.args[0] == "a2"
+    call = handle.await_args
+    assert call is not None
+    assert call.args[0] == "a2"