Close serial port when disconnected to ensure clean reconnection

[sammdot]

In addition to the changes from #1560, this PR closes a serial port on error to handle this issue from #1054:

Now an exception in the run method is reported as an error to the system
and additionally the SerialStenotypeBase class does close the com port on
error.

Otherwise the com port resource might still be taken by plover upon
reconnect of the writer, and a different com port might be taken by the OS
and plover might not be able to reconnect to that machine.

Closes #1054.

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[pianohacker]

I've been running a fork to work around this issue for literal years. Thank you so much.