audiocore: Add async support

Rename the exising audiocore C module to _audiocore and create a new
Micropython wrapper module audiocore. This makes it easier to implement
async methods.
Add interrupt support to _audiocore that notifies core0 whenever data
has been consumed from the MP3 bitstream buffer.
Use this interrupt and an asyncio.ThreadSafeFlag to implement
audiocore.async_put which will play back the provided buffer, allowing
other async tasks to run while waiting for space in the bitstream
buffer.

software/boards/RPI_PICO_W/manifest.py

@@ -11,3 +11,5 @@ require("aiorepl")
 
 module("mfrc522.py", "../../lib/micropython-mfrc522/")
 module("microdot.py", "../../lib/microdot/src/microdot/")
+
+module("audiocore.py", "../../src/audiocore")