Return 400 when Serder validation fails

[rodolfomiranda]

This PR is related to #201

[pfeairheller]

The TraitCodex and MacOS problems are now fixed on main. Please rebase to pick them up.

[rodolfomiranda]

The TraitCodex and MacOS problems are now fixed on main. Please rebase to pick them up.

done

[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 92.78%. Comparing base (5f06007) to head (90c5432).
Report is 10 commits behind head on main.

❗ Current head 90c5432 differs from pull request most recent head 36fa77f. Consider uploading reports for the commit 36fa77f to get more accurate results

Files	Patch %	Lines
src/keria/app/credentialing.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #234      +/-   ##
==========================================
- Coverage   93.08%   92.78%   -0.30%     
==========================================
  Files          38       37       -1     
  Lines        7002     6990      -12     
==========================================
- Hits         6518     6486      -32     
- Misses        484      504      +20     

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

[2byrds]

LGTM. Thank you for the contribution.