Align pre-existing context manager methods with repo idiom

Apply the same `__enter__`/`__exit__` typing pattern that PR #145 uses
for `TaskHubGrpcClient` (and that `BlobPayloadStore` already follows)
to three pre-existing context managers that were either untyped or
shadowed a builtin:

* `AsyncTaskHubGrpcClient.__aenter__` now returns the concrete type and
  `__aexit__` takes `*args: object` with `-> None`.
* `TaskHubGrpcWorker.__enter__/__exit__` get the same treatment, also
  removing the `type` parameter that shadowed the builtin.
* `EntityLock.__enter__/__exit__` get the same treatment; the file
  already has `from __future__ import annotations` so the return
  annotation is the bare class name.

Behavior is unchanged: each `__exit__` still delegates to its existing
teardown method (`close`/`stop`/`_exit_critical_section`), so the
gRPC resiliency teardown added in PR #135 continues to flow through
`TaskHubGrpcClient.close()` unchanged.

No changelog entry: per the repo's contributor guidance, internal-only
type-annotation refactors with no externally observable behavior change
are excluded from the changelog.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Bernd Verst

durabletask/client.py

@@ -789,10 +789,10 @@ async def close(self) -> None:
                 await retired_channel.close()
             await self._channel.close()
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> "AsyncTaskHubGrpcClient":
         return self
 
-    async def __aexit__(self, exc_type, exc_val, exc_tb):
+    async def __aexit__(self, *args: object) -> None:
         await self.close()
 
     def _schedule_recreate(self) -> None:

durabletask/entities/entity_lock.py

@@ -12,8 +12,8 @@ class EntityLock:
     def __init__(self, context: OrchestrationContext):
         self._context = context
 
-    def __enter__(self):
+    def __enter__(self) -> EntityLock:
         return self
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
+    def __exit__(self, *args: object) -> None:
         self._context._exit_critical_section()

durabletask/worker.py

@@ -581,10 +581,10 @@ def maximum_timer_interval(self) -> timedelta | None:
         """Get the configured maximum timer interval for long timer chunking."""
         return self._maximum_timer_interval
 
-    def __enter__(self):
+    def __enter__(self) -> "TaskHubGrpcWorker":
         return self
 
-    def __exit__(self, type, value, traceback):
+    def __exit__(self, *args: object) -> None:
         self.stop()
 
     def _classify_stream_outcome(