Fixes multiple vacuum issues

[daveshanley]

• resolving-references fails to find $ref item by $id daveshanley/vacuum#798
• schema function triggering circular reference render failure daveshanley/vacuum#799

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.54%. Comparing base (91fc80f) to head (2a74657).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #515      +/-   ##
==========================================
+ Coverage   99.52%   99.54%   +0.02%     
==========================================
  Files         191      191              
  Lines       23466    23663     +197     
==========================================
+ Hits        23354    23555     +201     
+ Misses         69       66       -3     
+ Partials       43       42       -1     

Flag	Coverage Δ
unittests	99.54% <100.00%> (+0.02%)	⬆️

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