Function aur_install_body 

pub fn aur_install_body(flags: &str, n: &str) -> String

What: Build the common AUR install body that prefers paru and falls back to yay.

Input:

• flags: Full flag string forwarded to the helper (use aur_install_helper_flags for installs).
• n: Space-separated AUR package names only (must not include official/repo targets).

Output:

• Parenthesised shell snippet (if ... fi) without the trailing hold suffix.

Details:

• Prefers paru if available, otherwise falls back to yay.
• Shows error message if no AUR helper is found.