fix: allow comptime or non comptime fields in unconstrained for loops

[jfecher]

Related issue(s)

Resolves #

Description

The previous check for type checking unconstrained for loops erroneously always unified with a non-comptime Field which produced type errors when used with a comptime one.

This wasn't caught previously since numeric literals are polymorphically comptime and would just bind to CompTime::No previously. It would only trigger if using a variable which was explicitly declared with a comptime type like let a: comptime Field = 2;.

Summary of changes

Fixes the above check by unifying against a polymorphically comptime field instead of a non-comptime one.

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Documentation needs

• This PR requires documentation updates when merged.

Additional context