i believe you! but maybe @dhalbert can do a more 👁️ review

Thank you for doing all this work! The macros to manipulate bitmasks are a nice addition. At first I thought they were pre-existing, but I saw that you added them.

1. I merged the Pico-PIO-USB update. Could you update to the merge commit? Thanks.
2. I tested I2SOut on Feather RP2040. I happened to have a test program that played a tone. No sound comes out with this build. Feather RP2040 PropMaker would also be an easy test board.

test program: this was adapted from a test program someone else had supplied for testing something else entirely

import array
import audiocore
import audiobusio
import board
import math
import time


# I2S audio out
audio = audiobusio.I2SOut(board.D9, board.D10, board.D11)

# Generate one period of sine wave.
length = 8000 // 440
sine_wave = array.array("H", [0] * length)
for i in range(length):
    val = int(math.sin(math.pi * 2 * i / length) * (2 ** 15 - 1) + 2 ** 15)
    sine_wave[i] = val

sine_wave = audiocore.RawSample(sine_wave, sample_rate=8000)

while True:
    audio.play(sine_wave, loop=True)

    time.sleep(2)
    audio.stop()