fix: content type validation should be case insensitive

[hlavacekvit]

I ran into this in production: an old .NET app couldn't call our Huma-based service because it sends Content-Type: Application/Json (capitalized), and Huma responded with 415 Unsupported Media Type.

Media types are case-insensitive per RFC 9110 §8.3.1, but the format lookup (a.formats[ct]) is a case-sensitive map access, so Application/Json doesn't match the registered application/json.

Fixed by lowercasing the media-type token. Added a test as well

[wolveix]

Awesome find and fix, thanks @hlavacekvit!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.16%. Comparing base (fd8148e) to head (c9059e8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1052   +/-   ##
=======================================
  Coverage   93.16%   93.16%           
=======================================
  Files          23       23           
  Lines        4918     4919    +1     
=======================================
+ Hits         4582     4583    +1     
  Misses        272      272           
  Partials       64       64           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.