chore(ci): test TestModels using parameterized JUnit tests

[robin-aws]

Description of changes: Replaces the GitHub actions matrices with @ParameterizedTests that run the same commands for every discovered test model, unless explicitly marked as disabled.

There are several advantages to this:

• Makes it possible to run all tests locally much more easily, using standard JUnit tooling such as IntelliJ test support.
• Makes it more feasible to maintain branch protection that requires all checks, since the names won't change as test models are added or enabled for new targets.
• Ensures every test model is verified and tested against each supported language by default, unless marked as not supported yet, in which case it will be SKIPPED.
• More efficiently uses GHA runners by not requiring a separate runner for every individual test: the tests are sharded across a tunable number of runners. This also makes it more feasible to test on multiple OS' in the future, which will also increase the number of jobs.
• Opens the door for utilities like "update the patch files for every test model currently running against Rust".

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[robin-aws]

Those were all unintentional/temporary changes I neglected to undo. Fixed now (especially by applying the same changes for Rust).

Apologies for the sloppy PR, I don't do my usual review of changes before flipping out of draft.