quint/grammar: add support for optional leading hashbang line

[lucab]

This updates Quint grammar to support a leading hashbang (#!) line in spec files.
It allows using a spec file as a self-running script on Unix systems, as shown in SuperSpec.qnt.

• Tests added for any new code
• Entries added to the respective CHANGELOG.md for any new functionality

Closes #1500

[lucab]

/cc @bugarela for review.

I decided to follow JS approach and only carve a niche in the grammar for the first line, see https://github.com/tc39/proposal-hashbang for details.

[bugarela]

Thanks so much for taking the time and linking that proposal!
I just left a comment on the grammar. Also, it would be good to add an integration tests that calls ./testFixture/SuperSpec.qnt to test the overall hashbang behavior. It should be simple to add that to cli-tests.md, and you can run the integration tests with npm run integration - lmk if you need assistance with that or would rather have me take on from here.

[bugarela]

Using skip where tells ANTLR that we want to skip this token, wherever it appears, as it is the case with comments and whitespaces. However, in this case, we only want to allow this in the very first line, so we shouldn't skip it. I've tested this locally and confirmed that, in the current state, this will allow hasbangs in the middle of a file.

We can simply remove the -> skip here and move it closer to the other regular tokens (and away from the skipped ones).

[lucab]

Apologies, I'm not overly familiar with ANTLR grammars so I didn't realize that skip had such a side-effect.
I did the changes you suggested and also added a few unit tests to ensure that the hashbang rule only applies to the first line of the file.

[lucab]

Fixed grammar rules and rebased to latest main. Also added an integration test at the bottom of cli-tests.md to run the typechecking on SuperSpec.qnt via the hashbang on Unix.

[bugarela]

Looks great! Thanks again