Properly handle NAK frames and implement retries

[puddly]

This should significantly increase the reliability of communication and prevent what should have been simple ASH re-sends or timeouts from turning into full reconnects.

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This change exists in #606 already, which will be merged in the next release cycle.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (1c43536) 99.73% compared to head (eda3f2c) 99.58%.

❗ Current head eda3f2c differs from pull request most recent head 932cc02. Consider uploading reports for the commit 932cc02 to get more accurate results

Files	Patch %	Lines
bellows/uart.py	77.77%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #610      +/-   ##
==========================================
- Coverage   99.73%   99.58%   -0.16%     
==========================================
  Files          74       74              
  Lines        4987     5014      +27     
==========================================
+ Hits         4974     4993      +19     
- Misses         13       21       +8     

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