Function encode_ping 

pub fn encode_ping(tail: FeedPosition) -> Vec<u8> 

Encode the in-stream heartbeat carrying the primary’s tail: +PING <generation> <next_offset>\r\n.

use kevy_replicate::feed::FeedPosition;

assert_eq!(kevy_replicate::wire::encode_ping(FeedPosition::new(3, 9)), b"+PING 3 9\r\n");