[Core] Support async scheduling with uniproc executor (#24219)

Signed-off-by: Nick Hill <nhill@redhat.com>
Signed-off-by: Ronald1995 <ronaldautomobile@163.com>
Co-authored-by: Ronald1995 <ronaldautomobile@163.com>
Co-authored-by: Robert Shaw <114415538+robertgshaw2-redhat@users.noreply.github.com>

tests/v1/engine/test_engine_core.py

@@ -257,9 +257,13 @@ def test_engine_core_concurrent_batches(monkeypatch: pytest.MonkeyPatch):
         def execute_model(
             self,
             scheduler_output,
+            non_block=False,
         ) -> Future[ModelRunnerOutput]:
             """Make execute_model non-blocking."""
 
+            # DummyExecutor used only for testing async case.
+            assert non_block
+
             def _execute():
                 output = self.collective_rpc("execute_model",
                                              args=(scheduler_output, ))