fix: double validation errors

[skwair]

Description

This PR fixes a regression introduced in #705, described in #717.

While hardening test cases, I noticed that slices of uint8s were not supported, so I took the liberty to also add the implementation (in a separate commit though, which can be reverted if this was intentional).

Fixes #717

[danielgtaylor]

Thanks!

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.86%. Comparing base (b2dfa81) to head (644be26).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
huma.go	76.92%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #718      +/-   ##
==========================================
- Coverage   92.90%   92.86%   -0.05%     
==========================================
  Files          22       22              
  Lines        4963     4976      +13     
==========================================
+ Hits         4611     4621      +10     
- Misses        305      308       +3     
  Partials       47       47              

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