Function clean_keywords 

pub fn clean_keywords(keywords: &str) -> String

Cleans keywords by removing comments and extra whitespace (generic version).

This function works for any quantum chemistry program by removing:

• Lines starting with ‘#’ (full-line comments)
• Inline comments (text after ‘#’ on the same line as valid keywords)
• Empty lines
• Leading and trailing whitespace from each line

The remaining valid keywords are joined with single spaces.

Arguments

• keywords - The raw keyword string that may contain comments and extra whitespace

Returns

Returns a String containing cleaned keywords joined with single spaces.