feat(SwarmBuilder): make `with_bandwidth_logging` chainable

[mxinden]

Description

SwarmBuilder::with_bandwidth_logging allows adding a bandwidth logging to a tree of transports constructed via SwarmBuilder. It returns both the builder and the BandwidthSinks. That is not ideal as it breaks the builder chain.

This originally came up in #4120 (comment).

Motivation

A single continuous builder chain is more ergonomic.

Current Implementation

The current with_bandwidth_logging requires a two step builder flow:

rust-libp2p/libp2p/src/builder.rs

Lines 300 to 321 in 56cb08a

	let (builder, _bandwidth_sinks) = SwarmBuilder::with_new_identity()
	.with_tokio()
	.with_tcp(
	Default::default(),
	libp2p_tls::Config::new,
	libp2p_yamux::Config::default,
	)
	.unwrap()
	.with_quic()
	.with_dns()
	.unwrap()
	.with_relay_client(libp2p_tls::Config::new, libp2p_yamux::Config::default)
	.unwrap()
	.with_websocket(libp2p_tls::Config::new, libp2p_yamux::Config::default)
	.await
	.unwrap()
	.with_bandwidth_logging();
	let _: Swarm<MyBehaviour> = builder
	.with_behaviour(|_key, relay| MyBehaviour { relay })
	.unwrap()
	.build();
	}

See also #4626 (comment).

Are you planning to do it yourself in a pull request ?

No