feat(gossipsub): introduce backpressure

protocols/gossipsub/CHANGELOG.md

@@ -3,6 +3,13 @@
 - Attempt to publish to at least mesh_n peers when flood publish is disabled.
   See [PR 5578](https://github.com/libp2p/rust-libp2p/pull/5578).
 
+- Introduce back pressure and penalize slow peers. Drop stale messages that timeout before being
+  delivered.
+  See [PR 5595](https://github.com/libp2p/rust-libp2p/pull/5595).
+- Change `Behaviour::unsubscribe` and `Behaviour::report_message_validation_result`
+  to `bool` they don't need to be a `Result`.
+  See [PR 5595](https://github.com/libp2p/rust-libp2p/pull/5595).
+
 ## 0.47.0
 
 <!-- Update to libp2p-swarm v0.45.0 -->

protocols/gossipsub/Cargo.toml

@@ -14,6 +14,7 @@ categories = ["network-programming", "asynchronous"]
 wasm-bindgen = ["getrandom/js"]
 
 [dependencies]
+async-channel = "2.3.1"
 asynchronous-codec = { workspace = true }
 base64 = "0.22.1"
 byteorder = "1.5.0"
@@ -22,6 +23,7 @@ either = "1.11"
 fnv = "1.0.7"
 futures = { workspace = true }
 futures-ticker = "0.0.3"
+futures-timer = "3.0.2"
 getrandom = "0.2.15"
 hex_fmt = "0.3.0"
 web-time = { workspace = true }