Function yield_callback

tests/test-scheduler-basic-thorough.cpp:247–252

* @brief Callback function for yield test * * Yields to multi_step_callback_2 for step-by-step processing. */

 * Yields to multi_step_callback_2 for step-by-step processing.
 */
void yield_callback() {
    test_output.push_back("step_1");
    if (global_yield_task) {
        global_yield_task->yield(&multi_step_callback_2);
    }
}

/**
 * @brief Callback function for yield once test