pybricks.common: Add new BLE class.

This adds a new BLE class that is used for connectionless broadcasting/
observing on hubs with built-in Bluetooth Low Energy.

Also see https://github.com/pybricks/pybricks-micropython/pull/158.

examples/pup/hub_common/ble_broadcast.py

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+# ThisHub = MoveHub CityHub TechnicHub PrimeHub EssentialHub
+from pybricks.hubs import ThisHub
+from pybricks.pupdevices import Motor
+from pybricks.parameters import Port
+from pybricks.tools import wait
+
+# Initialize the hub.
+hub = ThisHub(broadcast_channel=1)
+
+# Initialize the motors.
+left_motor = Motor(Port.A)
+right_motor = Motor(Port.B)
+
+while True:
+    # Read the motor angles to be sent to the other hub.
+    left_angle = left_motor.angle()
+    right_angle = right_motor.angle()
+
+    # Set the broadcast data and start broadcasting if not already doing so.
+    hub.ble.broadcast(left_angle, right_angle)
+
+    # Broadcasts are only sent every 100 milliseconds, so there is no reason
+    # to call the broadcast() method more often than that.
+    wait(100)

examples/pup/hub_common/ble_observe.py

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+# ThisHub = MoveHub CityHub TechnicHub PrimeHub EssentialHub
+from pybricks.hubs import ThisHub
+from pybricks.pupdevices import Motor
+from pybricks.parameters import Color, Port
+from pybricks.tools import wait
+
+# Initialize the hub.
+hub = ThisHub(observe_channels=[1])
+
+# Initialize the motors.
+left_motor = Motor(Port.A)
+right_motor = Motor(Port.B)
+
+while True:
+    # Receive broadcast from the other hub.
+
+    data = hub.ble.observe(1)
+
+    if data is None:
+        # No data has been received in the last 1 second.
+        hub.light.on(Color.RED)
+    else:
+        # Data was received and is less that one second old.
+        hub.light.on(Color.GREEN)
+
+        # *data* contains the same values in the same order
+        # that were passed to hub.ble.broadcast() on the
+        # other hub.
+        left_angle = data[0]
+        right_angle = data[1]
+
+        # Make the motors on this hub mirror the position of the
+        # motors on the other hub.
+        left_motor.track_target(left_angle)
+        right_motor.track_target(right_angle)
+
+    # Broadcasts are only sent every 100 milliseconds, so there is
+    # no reason to call the observe() method more often than that.
+    wait(100)