[Documentation] fix asyncio Server and Channel stop() method documentation (#35946)

The stop/cancel methods actually wait if a grace period is specified, and do not "return immediately":

* 5227db884d/src/python/grpcio/grpc/_cython/_cygrpc/aio/server.pyx.pxi (L1060-L1063)
* 5227db884d/src/python/grpcio/grpc/aio/_channel.py (L444)
* 5227db884d/src/python/grpcio/grpc/_server.py (L1253)

Closes #35946

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35946 from Tasssadar:fix_grpc_stop_docs 1bafaa1eeb
PiperOrigin-RevId: 621230612

src/python/grpcio/grpc/__init__.py

@@ -1500,8 +1500,9 @@ class Server(abc.ABC):
 
         This method immediately stop service of new RPCs in all cases.
 
-        If a grace period is specified, this method returns immediately
-        and all RPCs active at the end of the grace period are aborted.
+        If a grace period is specified, this method waits until all active
+        RPCs are finished or until the grace period is reached. RPCs that haven't
+        been terminated within the grace period are aborted.
         If a grace period is not specified (by passing None for `grace`),
         all existing RPCs are aborted immediately and this method
         blocks until the last RPC handler terminates.

src/python/grpcio/grpc/aio/_base_channel.py

@@ -209,10 +209,11 @@ class Channel(abc.ABC):
         This method immediately stops the channel from executing new RPCs in
         all cases.
 
-        If a grace period is specified, this method wait until all active
-        RPCs are finshed, once the grace period is reached the ones that haven't
-        been terminated are cancelled. If a grace period is not specified
-        (by passing None for grace), all existing RPCs are cancelled immediately.
+        If a grace period is specified, this method waits until all active
+        RPCs are finished or until the grace period is reached. RPCs that haven't
+        been terminated within the grace period are aborted.
+        If a grace period is not specified (by passing None for grace),
+        all existing RPCs are cancelled immediately.
 
         This method is idempotent.
         """

src/python/grpcio/grpc/aio/_base_server.py

@@ -93,11 +93,12 @@ class Server(abc.ABC):
         This method immediately stops the server from servicing new RPCs in
         all cases.
 
-        If a grace period is specified, this method returns immediately and all
-        RPCs active at the end of the grace period are aborted. If a grace
-        period is not specified (by passing None for grace), all existing RPCs
-        are aborted immediately and this method blocks until the last RPC
-        handler terminates.
+        If a grace period is specified, this method waits until all active
+        RPCs are finished or until the grace period is reached. RPCs that haven't
+        been terminated within the grace period are aborted.
+        If a grace period is not specified (by passing None for grace), all
+        existing RPCs are aborted immediately and this method blocks until
+        the last RPC handler terminates.
 
         This method is idempotent and may be called at any time. Passing a
         smaller grace value in a subsequent call will have the effect of

src/python/grpcio/grpc/aio/_server.py

@@ -131,11 +131,12 @@ class Server(_base_server.Server):
         This method immediately stops the server from servicing new RPCs in
         all cases.
 
-        If a grace period is specified, this method returns immediately and all
-        RPCs active at the end of the grace period are aborted. If a grace
-        period is not specified (by passing None for grace), all existing RPCs
-        are aborted immediately and this method blocks until the last RPC
-        handler terminates.
+        If a grace period is specified, this method waits until all active
+        RPCs are finished or until the grace period is reached. RPCs that haven't
+        been terminated within the grace period are aborted.
+        If a grace period is not specified (by passing None for grace), all
+        existing RPCs are aborted immediately and this method blocks until
+        the last RPC handler terminates.
 
         This method is idempotent and may be called at any time. Passing a
         smaller grace value in a subsequent call will have the effect of