fix: No longer error on INT_MIN globals

[jfecher]

Description

Problem*

Resolves #7506
Resolves #7324

This PR also possibly improves some error messages which previously displayed negative integer values as a negated field value (a large number) - these will now show an actual negative sign and integer value. I don't expect this to be a noticeable change however since there's a check on FieldElement::display to just display the value as negative if that value is smaller (in terms of string characters).

Summary*

Allow INT_MIN globals by properly handling negatives by refactoring the frontend to use SignedField instead of FieldElement, bool pairs.

Additional Context

One advantage I noticed while using SignedField was that I was able to refactor several separate conversion functions we had (mostly in the interpreter) from SignedField to various signed and unsigned integer types into one place. Before we had written these conversions several times and some handled INT_MIN properly while others did not. Now there are conversion methods on SignedField itself.

Some future improvements we could do that I did not tackle in this PR:

• Type::Constant still holds a FIeldElement rather than a SignedField. I think refactoring it to handle negatives was beyond the scope of this PR, although theoretically it should be easier in the future once we have the following point.
• We have several repeated methods for checking if a field value fits in a desired type. We could refactor these to just one method. (There is at least one in SSA and one for Type::Constant although the later is only on Fields). This feels like something that should be on SignedField itself (sans error reporting).

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[asterite]

Looks great! I left a couple of comments.

[asterite]

Sorry, scrolling through the page or something I clicked "Update branch" though it wasn't needed...