Function apply_fixes_to_content 

pub fn apply_fixes_to_content(content: &str, fixes: &[&Fix]) -> (String, usize)

Apply fixes to content string.

All fixes (both line-based and offset-based) are normalized to offset-based, then applied in reverse order to avoid index shifts. Overlapping fixes are skipped.

Returns (modified_content, number_of_fixes_applied).