Fix run_worker typing to support async def callables under mypy stric…

[Arghyann]

Description

This PR resolves issue #6386 by updating the WorkType type alias and overloading run_worker on DOMNode to prevent mypy type-inference failures when passing async def callables.

Root Cause:
In strict mode, mypy type-checks async def functions as returning Coroutine[Any, Any, ReturnType]. Since WorkType originally required Coroutine[None, None, ReturnType], it failed. Simply widening WorkType to Coroutine[Any, Any, ResultType] is insufficient because mypy's generic type inference conflicts when matching a callable return type against both Callable[[], Coroutine[Any, Any, ResultType]] and Callable[[], ResultType], causing it to infer ResultType as Never.

Fix:

1. Updated WorkType to accept Coroutine[Any, Any, ResultType] instead of Coroutine[None, None, ResultType].
2. Added three @overload signatures for run_worker in DOMNode to evaluate the callable/awaitable structures independently.
3. Updated the run_worker implementation signature to accept WorkType[Any] and return Worker[Any] to allow the overloads to drive the external type-checking.

Link to issue or discussion

Fixes #6386

Testing

• Verified that strict mypy checking passes on user reproduction files.
• Ran all existing worker unit tests via pytest tests/workers/ and verified they pass successfully.