Function get_aur_json_changes 

pub fn get_aur_json_changes(pkg_name: &str) -> Option<String>

What: Get cached JSON changes for an AUR package.

Inputs:

• pkg_name: Package name to look up.

Output:

• Some(String) with change description if changes were detected; None otherwise.

Details:

• Returns changes that were detected during the last fetch_aur_versions call.