Provide a no-op default implementation of serial port listing

[puddly]

The majority of platforms do not actually implement serial port listing. It's unnecessary verbosity to require them to provide an implementation of both functions that return a typed empty list.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.46%. Comparing base (4242e3e) to head (60bdbdb).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #66      +/-   ##
==========================================
- Coverage   90.49%   90.46%   -0.03%     
==========================================
  Files          19       19              
  Lines        3145     3137       -8     
==========================================
- Hits         2846     2838       -8     
  Misses        299      299              

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