MBT: Use modelator crate

[vitorenesduarte]

Closes: #761

Description

With this PR, we start using modelator, a model-based testing tool being developed at Informal. In particular:

• the following files were removed as their functionality is now provided by modelator:
  • modules/tests/executor/modelator.rs
  • modules/tests/support/model_based/gen_tests.py
• all static files in modules/tests/support/model_based/tests/ representing the tests generated by the model checkers are now generated on the fly (there are plans to cache them (see Add caching of model checking results modelator#27), which will speed up the developer experience when using modelator, but it won't improve CI times)

This PR currently relies on an unreleased version of modelator. This will be fixed by a follow-up PR (containing other improvements) once we do a proper release of modelator later this week.

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For contributor use:

• Updated the Unreleased section of CHANGELOG.md with the issue.
• If applicable: Unit tests written, added test to CI.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments.
• Re-reviewed Files changed in the Github PR explorer.

[romac]

Awesome 🎉

[romac]

@vitorenesduarte Can you please update the changelog before we merge?

[vitorenesduarte]

@vitorenesduarte Can you please update the changelog before we merge?

@romac Not sure it's a requirement for this kind of PRs, but I opened an issue and linked it in the changelog. Please check if this is okay.

[romac]

Perfect, thanks!