Add conformance testing for ENACT

[Soupstraw]

Description

Adds conformance testing for the ENACT rule. Because the environment of ENACT is the unit type, I had to add associated types to ExecSpecRule that enable overwriting the types that the constrained generator generates as long as there's a way to inject that type into the environment/state/signal that we need in order to run the rule. With this change we should be able to get rid of ExecContext at some point when we get to refactoring the conformance tests.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[lehins]

Could you please try removing all of those Inject x x instances in favor of #4350 approach. I think it would be much cleaner that way. (Side note observation: it would have been nice if it was a separate commit that introduced those instances, which would allow to revert all that work much easier)