Function fix_html_comment_fences 

pub fn fix_html_comment_fences(s: &str) -> String

Fixes HTML comment closing fences to prevent content loss.

According to CommonMark, HTML block type 2 (comments) ends with the line containing -->. This means any text on the same line after --> is included in the HTML block and would be discarded by markdown parsers that ignore HTML blocks.

This function inserts a newline after --> when followed by non-whitespace content, ensuring the trailing text is parsed as regular markdown.

Examples

use quillmark_core::normalize::fix_html_comment_fences;

// Text on same line as --> is moved to next line
assert_eq!(
    fix_html_comment_fences("<!-- comment -->Some text"),
    "<!-- comment -->\nSome text"
);

// Already on separate line - no change
assert_eq!(
    fix_html_comment_fences("<!-- comment -->\nSome text"),
    "<!-- comment -->\nSome text"
);

// Only whitespace after --> - no change needed
assert_eq!(
    fix_html_comment_fences("<!-- comment -->   \nSome text"),
    "<!-- comment -->   \nSome text"
);

// Multi-line comments with trailing text
assert_eq!(
    fix_html_comment_fences("<!--\nmultiline\n-->Trailing text"),
    "<!--\nmultiline\n-->\nTrailing text"
);