Work out best way to handle reading large SysEx messages

[kevinjwalters]

Not of immediate concern but SysEx can be very big so need to work out what can be done here after first implementation for #3 , particularly taking into account memory limitations of various hardware CircuitPython runs on.

[kevinjwalters]

#3 will now at least parse past them although this may take a while if they are huge given the default read buffer size of 30.

[kevinjwalters]

There's some interest expressed in adafruit/circuitpython#2245 (comment) in reading SysEx messages. It also mentions a common practice of a "2 byte" (14bit?) length field.

Worth looking at design patterns for handling rare large messages - this might be a different approach to the regular small MIDI messages.

[kevinjwalters]

Winterbloom SmolMIDI supports SysEx: https://github.com/wntrblm/Winterbloom_SmolMIDI#system-exclusive-messages