HTEX submit returns type-aware future

Rather than a stock Future, that typing doesn't know will have a
`.parsl_executor_task_id` attached, formalize the attribute with a subclass.

Author: khk-globus

parsl/executors/high_throughput/executor.py

@@ -160,6 +160,12 @@
 """  # Documentation for params used by both HTEx and MPIEx
 
 
+class HTEXFuture(Future):
+    def __init__(self, task_id) -> None:
+        super().__init__()
+        self.parsl_executor_task_id = task_id
+
+
 class HighThroughputExecutor(BlockProviderExecutor, RepresentationMixin, UsageInformation):
     __doc__ = f"""Executor designed for cluster-scale
 
@@ -670,7 +676,7 @@ def _hold_block(self, block_id):
                 logger.debug("Sending hold to manager: {}".format(manager['manager']))
                 self._hold_manager(manager['manager'])
 
-    def submit(self, func, resource_specification, *args, **kwargs):
+    def submit(self, func: Callable, resource_specification: dict, *args, **kwargs) -> HTEXFuture:
         """Submits work to the outgoing_q.
 
         The outgoing_q is an external process listens on this
@@ -702,8 +708,7 @@ def submit(self, func, resource_specification, *args, **kwargs):
             args_to_print = tuple([ar if len(ar := repr(arg)) < 100 else (ar[:100] + '...') for arg in args])
             logger.debug("Pushing function {} to queue with args {}".format(func, args_to_print))
 
-        fut = Future()
-        fut.parsl_executor_task_id = task_id
+        fut = HTEXFuture(task_id)
         self.tasks[task_id] = fut
 
         try: