usb-midi-device crashes esp32-s3 when OUT USB packets sent at line rate

Splitting this issue out from #1158 where it was independently discovered by @agatti while investigating a related issue.

The issue can be reproduced by setting up a CPython program that transmits MIDI data to the device as quickly as possible. For example:

import rtmidi2
out = rtmidi2.MidiOut()
# Port 1 is 'Espressif Device:Espressif Device MIDI 1 24:0' in my case
out.open_port(1)
while True:
    out.send_pitchbend(0, 0)  # channel, pitch
    out.send_noteon(0, 48, 100)
    out.send_noteoff(0, 48)
    print(".", end="")

(Note that only the second two messages are currently processed by the MIDI device class, pitchbend messages are discarded.)

If running midi_example.py on the ESP32-S3, the exhibited behaviour is a few messages may be processed normally and then the handler fails with nonsense errors such as:

Traceback (most recent call last):
  File "usb/device/midi.py", line 168, in _on_rx
  File "usb/device/core.py", line 859, in pend_read
AttributeError: 'Buffer' object has no attribute '_b'
Traceback (most recent call last):
  File "usb/device/core.py", line 342, in _xfer_cb
  File "usb/device/midi.py", line 156, in _rx_cb
  File "usb/device/core.py", line 827, in finish_write
AttributeError: 'Buffer' object has no attribute '_b'

and/or possibly a hard crash.

Reproduce the failure with midi_example.py on an ESP32-S3 using the provided rtmidi2 line-rate sender. Start by tracing the receive and transfer callbacks in usb/device/midi.py and usb/device/core.py, especially the paths shown in the traceback. Done means sustained MIDI input no longer produces Buffer attribute errors or a hard crash.