This working on micropython/micropython-lib#503 I ran into the limitation that while the _thread.Lock.acquire() function supports the waitflag argument, it doesn't handle the timeout arg - while you can pass it it's silently ignored and instead blocks forever.

This PR adds support for the timeout arg. It does so in a fairly naive way I feel... but it does work.

1. try to get lock (unblocking)
2. if success, return True
3. if fail, sleep 1ms
4. if timeout expired, return False
5. else go back to 1.

Ref: https://docs.python.org/3/library/_thread.html#thread.lock.acquire

Similarly the test is not exactly best practice, what with having a static sleep in the middle, but it does test the behaviour.