Store the NoiseKey in peers.rs instead of collection.rs

[tomaka]

Step towards #44

Right now, the NoiseKey is stored in collection.rs within an Arc. This Arc is shared with all the background tasks.

This PR removes the NoiseKey from collection.rs, and you must now pass a &NoiseKey every time you add a connection to the collection. This allows using multiple different noise keys if desired.

The NoiseKey is now stored in peers.rs. Eventually, the plan is to move it to service.rs or even outside.
Unfortunately, peers.rs might be a bit of a blocker, because the same remote peer might open multiple substreams towards the multiple local identities without it being a protocol violation.
Even if peers.rs turns out to be a blocker, the change in this PR is good even in isolation.

As part of this change, we now provide the NoiseKey immediately when initializing a single stream handshake, so that we can pass a &NoiseKey by reference at initialization rather than having to store it by value and load it later.

[tomaka]

I've pushed a small side-change that replaces Box<NoiseHandshake> with NoiseHandshake.
This is because NoiseHandshake now contains a Box<NoiseHandshakeInner> rather than the fields directly.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

---

 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────
       -4966 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::next_event::h02c3036cf0bd0c28
       +4966 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::next_event::h474b47a75eea3f32
       -3528 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::next_event::h6273e3510799f587
       +3528 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::next_event::h85ba55eb53de2f5b
       -2120 ┊ smoldot::libp2p::connection::single_stream_handshake::HealthyHandshake::read_write::ha74c0141a53f7d5b
       +2047 ┊ smoldot::libp2p::connection::single_stream_handshake::HealthyHandshake::read_write::hbdc5b44629a32efc
       -1099 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::set_peer_notifications_out_desired::h15c965098f728fa3
       +1099 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::set_peer_notifications_out_desired::h338dfb16f365001e
        -764 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::new::he589a13cf9417721
        -752 ┊ smoldot::libp2p::collection::multi_stream::MultiStreamConnectionTask<TNow,TSubId>::new::heb811e910b2b79e7
        +716 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::new::h131dda455042e670
        -659 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::new::h1c5e359e61382ad1
        +655 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::new::h64196d573c9d0b56
        +633 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::insert_multi_stream::h7ecd2a1ab15bbdbb
        +538 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::close_out_notification::h5207b05af76e6cc0
        -538 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::close_out_notification::h52d7b2f6d9943e38
        +491 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::try_clean_up_peer::h92efec87167aa809
        -491 ┊ smoldot::libp2p::peers::Peers<TConn,TNow>::try_clean_up_peer::hcc15993d95f378a3
        -450 ┊ smoldot::libp2p::collection::Network<TConn,TNow>::insert_single_stream::h112cc92e3687c4ca
        +437 ┊ smoldot::libp2p::collection::multi_stream::MultiStreamConnectionTask<TNow,TSubId>::new::h534a70dc3c223380
        -529 ┊ ... and 173 more.
       -1127 ┊ Σ [193 Total Rows]