Create network_utils crate (#7761)

Anchor currently depends on `lighthouse_network` for a few types and utilities that live within. As we use our own libp2p behaviours, we actually do not use the core logic in that crate. This makes us transitively depend on a bunch of unneeded crates (even a whole separate libp2p if the versions mismatch!)


  Move things we require into it's own lightweight crate.


Co-Authored-By: Daniel Knopik <daniel@dknopik.de>

testing/execution_engine_integration/src/nethermind.rs

@@ -1,12 +1,12 @@
 use crate::build_utils;
 use crate::execution_engine::GenericExecutionEngine;
 use crate::genesis_json::nethermind_genesis_json;
+use network_utils::unused_port::unused_tcp4_port;
 use std::env;
 use std::fs;
 use std::path::{Path, PathBuf};
 use std::process::{Child, Command, Output};
 use tempfile::TempDir;
-use unused_port::unused_tcp4_port;
 
 /// We've pinned the Nethermind version since our method of using the `master` branch to
 /// find the latest tag isn't working. It appears Nethermind don't always tag on `master`.