Fix BCH/RS decoder caching bug

[mhostetter]

Fixes #483

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (08e4358) 96.33% compared to head (cf9d8b4) 96.33%.

Additional details and impacted files

@@              Coverage Diff               @@
##           release/0.3.x     #484   +/-   ##
==============================================
  Coverage          96.33%   96.33%           
==============================================
  Files                 46       46           
  Lines               5833     5842    +9     
==============================================
+ Hits                5619     5628    +9     
  Misses               214      214           

Impacted Files	Coverage Δ
src/galois/_codes/_bch.py	97.56% <100.00%> (+0.03%)	⬆️
src/galois/_codes/_reed_solomon.py	95.41% <100.00%> (+0.03%)	⬆️
src/galois/_domains/_function.py	97.10% <100.00%> (+0.08%)	⬆️

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