cache validation and avoid re-encoding

[daveshanley]

Schema rendering is expensive; this is an attempt to reduce the cost!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.61%. Comparing base (846c366) to head (dc85f5b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #239      +/-   ##
==========================================
+ Coverage   97.60%   97.61%   +0.01%     
==========================================
  Files          56       56              
  Lines        5256     5289      +33     
==========================================
+ Hits         5130     5163      +33     
  Misses        126      126              

Flag	Coverage Δ
unittests	97.61% <100.00%> (+0.01%)	⬆️

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