It is possible for print functions to raise an exception, so we need to
catch this when printing a final exception since the nlr stack is empty
at that point and would otherwise cause a crash.

Add a new function to convert PBIO error codes to MicroPython errnos.
This works similar to pb_assert(), but does not raise an exception.
There are some cases where we need to convert PBIO errors to errnos
without raising an exception, such as when implementing the stream
protocol.

Add a new stream object that uses the Pybricks Profile stdin/stdout over
Bluetooth. This is available a hub.bluetooth.io and can be used to
send and receive data over Bluetooth even when something else is used
for sys.stdin/stdout (e.g. USB).

Pull in changes to allow mutable sys.stdin, sys.stdout, and sys.stderr.

Change the sys.stdin, sys.stdout, and sys.stderr objects to be mutable
so that they can be replaced with USB stdio when available on hubs that
support it.

Add transport parameter to pbsys_command() so that it can distinguish
between commands received over USB and Bluetooth.

Copy the ring buffer logic from bluetooth to usb_stm32.c so that we
can get stdin commands over USB working.

Add a new USB stream type that can be used for stdin, stdout, and stderr
over USB. For now, this just lives at hub.usb.io.

Implement the Pybricks Profile event subscription flag.

This saves us from trying to send messages to the host when there is no
app running to receive them. Previously, trying to write to stdout
would block forever because of this.

The 5 millisecond timeout is arbitrary. Wireshark shows that the OUT
endpoint is being serviced in less than 1 ms, so this should be plenty
of time even if some hosts are an order of magnitude slower. We don't
want to make it too big because it will delay user programs for this
long and we don't want to mess up someone's control loop too badly.

Pass the transport type that requested the user program to start to
the MicroPython launcher to allow it to select the appropriate default
stdio stream (USB or Bluetooth).

Now that USB is mostly working, we can enable it by default on SPIKE
Essential and Prime hubs.