extmod/uasyncio: Implement Loop.stop() to stop the event loop.

tests/extmod/uasyncio_loop_stop.py

@@ -0,0 +1,45 @@
+# Test Loop.stop() to stop the event loop
+
+try:
+    import uasyncio as asyncio
+except ImportError:
+    try:
+        import asyncio
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+
+async def task():
+    print("task")
+
+
+async def main():
+    print("start")
+
+    # Stop the loop after next yield
+    loop.stop()
+
+    # Check that calling stop() again doesn't do/break anything
+    loop.stop()
+
+    # This await should stop
+    print("sleep")
+    await asyncio.sleep(0)
+
+    # Schedule stop, then create a new task, then yield
+    loop.stop()
+    asyncio.create_task(task())
+    await asyncio.sleep(0)
+
+    # Final stop
+    print("end")
+    loop.stop()
+
+
+loop = asyncio.get_event_loop()
+loop.create_task(main())
+
+for i in range(3):
+    print("run", i)
+    loop.run_forever()

tests/extmod/uasyncio_loop_stop.py.exp

@@ -0,0 +1,7 @@
+run 0
+start
+sleep
+run 1
+run 2
+task
+end