feat(stubs)!: add stubs for RustClosure

[Xenira]

Fixes: #373
BREAKING CHANGE: New field variadic added to Parameter struct.

Description

Added basic stubs for rust closure. This will always be included if the closure feature is enabled.

No argument information, as that is not rly available, but better than having no stubs.

Checklist

Check the boxes that apply (put an x in the brackets, like [x]). You can also check boxes after the PR is created.

• I have read the contribution guidelines.
• I have added tests that prove my code works as expected.
• I have added documentation if applicable.
• I have added a migration guide if applicable.

❤️ Thank you for your contribution!

[coveralls]

Pull Request Test Coverage Report for Build 16274060216

Details

• 13 of 15 (86.67%) changed or added relevant lines in 3 files are covered.
• 58 unchanged lines in 3 files lost coverage.
• Overall coverage remained the same at 22.552%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/describe/stub.rs	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/args.rs	7	81.82%
src/describe/mod.rs	8	89.04%
src/describe/stub.rs	43	7.69%

Totals
Change from base Build 16273331616:	0.0%
Covered Lines:	882
Relevant Lines:	3911

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💛 - Coveralls

[Xenira]

As enums introduced a similar bc we can merge this.