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: Flag string forwarded to the helper (e.g. -S --needed).
• n: Space-separated package names to install.

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.