fix: check the argument count of generic types

[jfecher]

Related issue(s)

Resolves the first part of #969

Description

Summary of changes

This PR issues an error when a type constructor is given an incorrect number of generic arguments. If these are not checked, we later fail an assert while instantiating struct types later on during type checking. To ensure we do not hit this assert even in the presence of bad input, we resize the generics vector on error. Either truncating it or filling it with fresh type variables until it is the desired size.

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.