Function increase_archlinux_backoff 

pub fn increase_archlinux_backoff(retry_after_seconds: Option<u64>)

What: Increase backoff delay for archlinux.org after a failure or rate limit.

Inputs:

• retry_after_seconds: Optional Retry-After value from server (in seconds)

Output: None

Details:

• If Retry-After is provided, uses that value (capped at maximum delay).
• Otherwise, doubles the current backoff delay (exponential backoff).
• Caps at maximum delay (60 seconds).
• Increments consecutive failure counter.