Remove test/models from repo; generate at test time

[rafabench]

Summary

• Remove committed test/models/ files from the repository
• Models are now generated by generate_models.jl during test runs via include() in runtests.jl
• Add test/models/ to .gitignore and Random to test extras

Test plan

• All 121 tests pass locally with Pkg.test()
• CI passes on all matrix entries

🤖 Generated with Claude Code

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.66%. Comparing base (0fb41a6) to head (88982c1).
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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #10   +/-   ##
=======================================
  Coverage   72.66%   72.66%           
=======================================
  Files          10       10           
  Lines         578      578           
=======================================
  Hits          420      420           
  Misses        158      158           

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