feat(cli): add support for configuring outgoing TTL and hop limit

Introduce a `--ttl` flag to allow users to set the IPv4 TTL or IPv6 hop limit, providing control over packet lifespan and helping diagnose network topology issues.

crates/irtt-client/src/config.rs

@@ -4,6 +4,7 @@ use irtt_proto::{Clock, ReceivedStats, StampAt};
 
 pub(crate) const DEFAULT_PORT: u16 = 2112;
 pub const MAX_DSCP_CODEPOINT: u8 = 63;
+pub const MAX_TTL: u32 = 255;
 pub const MAX_SERVER_FILL_BYTES: usize = 32;
 pub(crate) const DEFAULT_DURATION: Duration = Duration::from_secs(3);
 pub(crate) const DEFAULT_INTERVAL: Duration = Duration::from_secs(1);