feat: Adds invisible character detection logic and updates tests

[CristopherAguilar10]

This PR will add in invisible character detection functionality in code-expressions to the Cairo plugin.

Invisible Character and Whitespaces detection:

• The Function check_invisible_characters is implemented and performs the following checks in the Expr:
• Whitespaces: a warning of (Severity::Warning) if present.
• Invisible characters: error (Severity::Error) on C-style string literals like\u{200B}, \u{00AD}, \u{200C}, \u{200D}, \u{202C}, \u{FEFF}.

Motivation:

• The invisible kind of characters, like zero-width space, can create bugs that are impossible to trace in the code. This change enables the detection of such unwanted characters and possibly a warning/blocking their usage in code to guarantee the quality of source code.

Diagnostic Messages Add following two diagnostic messages:

• "Whitespace detected.": Whenever whitespace is detected.
• "Invisible character detected.": When invisible characters are detected.

[0xLucqs]

check the test file it's full of unrelated diagnostics

[CristopherAguilar10]

@0xLucqs, could you check the changes, thanks  🚀