Add API to terminate and await termination (#549)

To make it easier for the caller to do both regardless of whether source is sync or async.

[ML-8738](https://iguazio.atlassian.net/browse/ML-8738)

storey/sources.py

@@ -175,9 +175,17 @@ def emit(
         self._emit_fn(event)
         return awaitable_result
 
-    def terminate(self):
-        """Terminates the associated flow."""
+    def terminate(self, wait=False):
+        """
+        Terminates the associated flow.
+
+        :param wait: Whether to wait for the flow to terminate before returning.
+
+        :returns: None if wait=False. If wait=True, the termination result will be returned.
+        """
         self._emit_fn(_termination_obj)
+        if wait:
+            return self._await_termination_fn()
 
     def await_termination(self):
         """Awaits the termination of the flow. To be called after terminate. Returns the termination result of the
@@ -482,9 +490,17 @@ async def emit(
                 raise result
             return result
 
-    async def terminate(self):
-        """Terminates the associated flow."""
+    async def terminate(self, wait=False):
+        """
+        Terminates the associated flow.
+
+        :param wait: Whether to wait for the flow to terminate before returning.
+
+        :returns: None if wait=False. If wait=True, the termination result will be returned.
+        """
         await self._emit_fn(_termination_obj)
+        if wait:
+            return await self.await_termination()
 
     async def await_termination(self):
         """

tests/test_flow.py

@@ -185,8 +185,7 @@ def test_offset_commit():
             event.shard_id = shard
             event.offset = offset
             controller.emit(event)
-    controller.terminate()
-    termination_result = controller.await_termination()
+    termination_result = controller.terminate(wait=True)
     assert termination_result == 330
 
     offsets = copy.copy(platform.offsets)
@@ -225,9 +224,8 @@ async def async_offset_commit():
     try:
         assert offsets == {("/", i): num_records_per_shard for i in range(num_shards)}
     finally:
-        await controller.terminate()
+        termination_result = await controller.terminate(wait=True)
 
-    termination_result = await controller.await_termination()
     assert termination_result == 330