[hiopy] Subtasks

Creating subtasks for the flush operation in hiopy.

python/coyote_py.cpp

@@ -104,6 +104,7 @@ PYBIND11_MODULE(coyote, m) {
     m.def("get_field_metadata", &get_field_metadata);
     m.def("run", &coyote_run, py::call_guard<py::gil_scoped_release>());
     m.def("init", &coyote_init, "group_name"_a, "nthreads"_a = 1);
+    m.def("add_task", &coyote_add_task, "task"_a, "prio"_a = 0);
     m.def("start_datetime", &coyote_start_datetime);
     m.def("end_datetime", &coyote_end_datetime);
     m.def("group_comm", []() { return MPI_Comm_c2f(coyote_group_comm()); });