feat: Validate fixed values

[tefra]

📒 Description

Until now we skipped parsing and validated fixed values, but this interferes with the parsing unions of classes with the same fields but with different fixed values.

Resolves #1012

🔗 What I've Done

Write a description of the steps taken to resolve the issue

💬 Comments

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🛫 Checklist

• Updated docs
• Added unit-tests
• Sample tests pass
• W3C tests pass

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (9be40c4) to head (73ddc8c).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1013   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          117       117           
  Lines         9188      9211   +23     
  Branches      2181      2186    +5     
=========================================
+ Hits          9188      9211   +23     

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