Fix type hints for http_server

[alexrudd2]

Eliminates 3 more errors.

pymodbus/server/simulator/http_server.py:141: error: Argument 2 to "ModbusSimulatorContext" has incompatible type "str"; expected "Dict[str, Callable[..., Any]]"  [arg-type]
pymodbus/server/simulator/http_server.py:178: error: No overload variant of "__setitem__" of "list" matches argument types "int", "str"  [call-overload]
pymodbus/server/simulator/http_server.py:178: note: Possible overload variants:
pymodbus/server/simulator/http_server.py:178: note:     def __setitem__(self, SupportsIndex, Callable[[Any, Any], Any], /) -> None
pymodbus/server/simulator/http_server.py:178: note:     def __setitem__(self, slice, Iterable[Callable[[Any, Any], Any]], /) -> None
pymodbus/server/simulator/http_server.py:181: error: Need type annotation for "call_list" (hint: "call_list: List[<type>] = ...")  [var-annotated]

[janiversen]

Your changes to get mypy working are VERY useful, but please try not to remove/change code without understanding it.

Your work is really appreciated and I try my best to help you understand the code, but it seems this batch of review involved a lot more than just satisfying mypy (I think about the comments I left in the datastore as well).

[janiversen]

LGTM, thanks.