fix: Avoid conflict with attributes named value when flattening extensions

[tefra]

📒 Description

When we flatten simple type extensions, we create a default text node value attr. If the model includes an attribute field with name "value", the whole thing fails.

Resolves #1084

🔗 What I've Done

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💬 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
0.0% Coverage on New Code
0.0% Duplication on New Code

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (dd587cd) to head (fb907cc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1085   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files          115       115           
  Lines         9276      9276           
  Branches      1417      1417           
=========================================
  Hits          9276      9276           

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