*: Fix clippy errors from upgrade to Rust 1.57 (#2365)

* core: Mark "unused" field with "_"

We need to keep this marker type to ensure that the type continues
to be required to be pinned.

* tranports/noise: Derive `Default` for `Config`

`false` is the default for `bool`, we can derive this.

* protocols/request-response: Remove unused fields

These are already included the `RequestResponseMessage::Request`
variant.

* *: Allow clippy's large-enum-variant lint

Tackling these suggestions would require performance measurement
which we don't want to do at this stage.

Co-authored-by: Max Inden <mail@max-inden.de>

protocols/identify/src/identify.rs

@@ -459,6 +459,7 @@ impl NetworkBehaviour for Identify {
 }
 
 /// Event emitted  by the `Identify` behaviour.
+#[allow(clippy::large_enum_variant)]
 #[derive(Debug)]
 pub enum IdentifyEvent {
     /// Identification information has been received from a peer.