Add `ttl` and `set_ttl` methods to TcpListener

Can `ttl` and `set_ttl` methods for `TcpListener` be implemented to enable getting and setting the TTL value of the underlying socket?

Start by locating the TcpListener implementation and tracing how it accesses the underlying socket. Check nearby socket-option tests or related listener methods, then verify that ttl and set_ttl can get and set the socket TTL value and that the behavior is covered by tests.

Written by the indexing model from the issue text.