feat: prevent duplicate validators in codegen

[perher]

This PR fixes a bug where duplicate validator methods could be created for types that were using subschemas with anyOf/allOf.

Proposed solution in PR is to perform a strict duplicate check in codegen and not emit methods if already emitted.

[codecov]

Codecov Report

❌ Patch coverage is 21.31148% with 48 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@37d54f2). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
tests/data/core/allOf/allOfNestedRefs.go	0.00%	48 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #510   +/-   ##
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  Coverage        ?   40.88%           
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  Files           ?       67           
  Lines           ?     5702           
  Branches        ?        0           
=======================================
  Hits            ?     2331           
  Misses          ?     3095           
  Partials        ?      276           

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