Add CI test for manually maintained tests.toml files

[senekor]

See here for the original idea.

Basically, some exercises don't lend themselves to generating tests based on a template. We still want to be sure that the tests.toml produced by configlet matches a manually maintained test file. For this purpose, we could have a test that parses the tests.toml (using toml crate) and checks that for each test, a function named make_ident(description) exists in the rust test file.

Some test names may differ, in which case rust_fn in tests.toml can be used to override make_ident(description).

[ellnix]

I'd like to try to implement this, I'll go ahead if you don't have any objections in the next few hours.

[senekor]

nope, go ahead 🙂