Avoid rebinding passed parameters

[puddly]

Fixes #96.

The underlying error is a bit subtle: we set exc to a default error if it is None (when the connection is closed gracefully) in order to flag future operations on the serial object. This unintentionally rebound exc and leaked the error to self._call_protocol_connection_lost(exc) as well.

This class of bug isn't flagged by mypy or ruff so I wrote a small custom pylint plugin to catch cases like this in addition to the new unit test for the underlying behavior.

[codecov]

Codecov Report

❌ Patch coverage is 98.41270% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.23%. Comparing base (f9f1bf2) to head (3c2297b).
⚠️ Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
serialx/common.py	97.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #98      +/-   ##
==========================================
- Coverage   92.23%   92.23%   -0.01%     
==========================================
  Files          22       22              
  Lines        3632     3631       -1     
==========================================
- Hits         3350     3349       -1     
  Misses        282      282              

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