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/lib.rs

@@ -14,7 +14,7 @@ mod timing;
 pub use client::Client;
 pub use config::{
     ClientConfig, NegotiationPolicy, RecvBudget, RunMode, SocketConfig, MAX_DSCP_CODEPOINT,
-    MAX_SERVER_FILL_BYTES,
+    MAX_SERVER_FILL_BYTES, MAX_TTL,
 };
 pub use error::{ClientError, EventSubscriptionError};
 pub use event::{