feat: improve malformed test attribute error

[asterite]

Description

Problem

Resolves #4676

Summary

In reality we were producing an error message for this snippet:

#[test(should_fail_with("Arrays not equal"))]
fn foo() {}

though the error message said that it couldn't find a test function. The reason is that the lexer couldn't parse the attribute contents well: it split the attribute contents when ( and ) were found and tried to match that to some expected format, but because here we have nested parentheses it didn't work. What I did is try to parse that by checking the first and last parentheses.

I also didn't know you could write #[test(should_fail)] so I added that as an LSP autocompletion.

Additional Context

I'm thinking that maybe the attribute contents should be parsed by lexing its contents. With that, we could also keep a nesting counter when [ and ] are found, to allow arrays in attributes (it's tricky without lexing the contents because [ might appear inside a string literal, etc.). But for now this slightly improves the current situation.

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.