Function repo_order 

pub fn repo_order(src: &Source) -> u8

What: Determine ordering weight for a package source.

Inputs:

• src: Package source to rank.

Output:

• Returns a u8 weight where lower values indicate higher priority.

Details:

• Used to sort results such that official repositories precede AUR, and core repos precede others.
• Order: core => 0, extra => 1, other official repos => 2, AUR => 3.
• Case-insensitive comparison for repository names.