Update game loop test logic to handle expected Arduino response

[nashirj]

In testfiles, in addition to the outgoing pi msg, we should specify the expected Arduino response. This will allow smoother automated testing.

To this end, it might be cleaner to separate out test file runner logic from the main game loop.

Also, the opcode generator GUI should be updated to include the expected response from the Arduino (where possible; some instructions like requesting current electromagnet position do not have a static response msg, but others do).

[nashirj]

[nashirj]

As part of this PR, fix logic so that the message is sent verbatim; don't parse the test message and then send a message accordingly, just send it directly.