Function cloudflare_soos::cf_priority_change_header

pub fn cf_priority_change_header(image: &[u8]) -> Result<(String, String)>

Assumes the priorities are:

• 50 = critical js/css, fonts + image metadata
• 30 = regular js/css, followed by other images + JPEG DC
• 20 = low-priority image bodies
• 10 = idle

Returns cf-priority and cf-priority-change