Function sync_repo_pkgnames 

pub fn sync_repo_pkgnames(repo: &str) -> Result<HashSet<String>, String>

What: Collect pkgname values from pacman -Sl <repo>.

Inputs:

• repo: Lowercase [repo] name (e.g. chaotic-aur).

Output:

• Set of package names or error.

Details:

• Ignores header lines and malformed rows.

Errors

• Returns an error when pacman cannot be executed, exits non-zero, or the repo is unknown.