Bugfix/E5CN-COM-PermissionError

[mslaffin]

On 11/25, noticed the following message appearing several times at the terminal (not in Messages & Errors log):
could not open port 'COM4': PermissionError(13, 'Access is denied.', None, 5)

[mslaffin]

Resolved the PermissionErrors that were stemming directly from PyModbus/pyserial's internal error handling, bypassing our logging system.

Still need to address timing issue that's leading to "Incomplete Message" errors. Note that these are still not fatal-- and I'm getting successful reads immediately after these appear.

[mslaffin]

This turned out to be a pretty stupid bug. I tried clearing any stale data upon connection in read_temperature using pyserial's reset_input_buffer() and immediately all the remaining errors went away.

Here's a log file showing clean communication with the E5CN (other equipment disconnected):
log_2024-12-02_18-06-22.txt

In this test I grabbed each of the thermocouples briefly to confirm it was responsive to changing temp. Here's what the log's output plot looks like after running the post-processor: