in_waiting missing from board.UART

[Fancy2209]

Board Name

Raspberry Pi Pico

Steps

1. Install MicroPython on the Pico
2. Install Blinka and the Adafruit_CircuitPython_GPS Lib
3. Connect the Adafruit Ultimate GPS Breakout to the Pico
4. Try to run gps_simpletest.py

Description

The board.UART implementation doesn't have in_waiting, which is used by the Adafruit CircuitPython GPS Library, preventing it from working on the Pico.
Closest related issue is #332

Additional information

I was able to successfully port the GPS library to pure MicroPython by making the in_waiting getter in the GPS lib return

result = self._uart.any()
return result if result == 0 else int(result / 8)

But I am not sure if that's the right way to handle this.

MicroPython is also missing time.struct_time and time.monotonic(), I replaced them by a List and time.time_ns() to be able to get the GPS lib to work, though I should probably open an issue or PR on the GPS Lib about that once this is fixed

[makermelissa]

Good call. I don't think busio.UART has been updated in a while because the linux boards are currently using PySerial separately. If would be good to do this at the same time as #332.