Improve validation logic

[mtmk]

Added more model validation and fixed DecodeClaims<T>() to decode any claims model including auth requests used in callouts.

[codecov]

Codecov Report

Attention: Patch coverage is 99.15254% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.73%. Comparing base (4a9a63c) to head (1d48d17).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/NATS.Jwt/ModelValidationExtensions.cs	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   76.88%   79.73%   +2.84%     
==========================================
  Files          48       49       +1     
  Lines         809      893      +84     
  Branches       63       81      +18     
==========================================
+ Hits          622      712      +90     
+ Misses        162      155       -7     
- Partials       25       26       +1     

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[aricart]

This looks good to me, but should make sure that anything you generate will be valid in the Go library... Also on the doc for the lib, it should say that the Go library performs many validation that this library doesn't.

[mtmk]

This looks good to me, but should make sure that anything you generate will be valid in the Go library... Also on the doc for the lib, it should say that the Go library performs many validation that this library doesn't.

good point. created #34 to track that