Warn when using defaults that aren't explict and not metadata

[benjeffery]

Fixes #766

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.18%. Comparing base (e3b2155) to head (8235f6f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #992   +/-   ##
=======================================
  Coverage   93.17%   93.18%           
=======================================
  Files          18       18           
  Lines        6374     6379    +5     
  Branches     1088     1088           
=======================================
+ Hits         5939     5944    +5     
  Misses        296      296           
  Partials      139      139           

Flag	Coverage Δ
C	93.18% <100.00%> (+<0.01%)	⬆️
python	95.53% <100.00%> (+<0.01%)	⬆️

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