Use structured concurrency to return the _actual_ error associated with sending a message

[NoahAndrews]

Currently, the status code returned by sendCANMessage() is just the most recent status of the sending thread, which is just the status of sending some previous message. Instead, sendCANMessage() should return some kind of promise-like object on which you can await the status of sending the actual provided message. Most likely we'd implement this using C++ coroutines.