feat(kad): make Distance private field public

make Distance private field (U256) public

So that some `network density` in Distance can be calculated as below:

```rust
let density = U256::MAX / U256::from(estimated_network_size);
let density_distance = Distance(estimated_distance);
```

Pull-Request: #5705.

Cargo.toml

@@ -83,7 +83,7 @@ libp2p-floodsub = { version = "0.45.0", path = "protocols/floodsub" }
 libp2p-gossipsub = { version = "0.48.0", path = "protocols/gossipsub" }
 libp2p-identify = { version = "0.46.0", path = "protocols/identify" }
 libp2p-identity = { version = "0.2.10" }
-libp2p-kad = { version = "0.47.0", path = "protocols/kad" }
+libp2p-kad = { version = "0.47.1", path = "protocols/kad" }
 libp2p-mdns = { version = "0.46.0", path = "protocols/mdns" }
 libp2p-memory-connection-limits = { version = "0.3.1", path = "misc/memory-connection-limits" }
 libp2p-metrics = { version = "0.15.0", path = "misc/metrics" }

protocols/kad/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.47.1
+
+- Expose Distance private field U256 to public.
+  See [PR 5705](https://github.com/libp2p/rust-libp2p/pull/5705).
+
 ## 0.47.0
 
 - Expose a kad query facility allowing specify num_results dynamicaly.

protocols/kad/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-kad"
 edition = "2021"
 rust-version = { workspace = true }
 description = "Kademlia protocol for libp2p"
-version = "0.47.0"
+version = "0.47.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

protocols/kad/src/kbucket/key.rs

@@ -35,7 +35,7 @@ use crate::record;
 
 construct_uint! {
     /// 256-bit unsigned integer.
-    pub(super) struct U256(4);
+    pub struct U256(4);
 }
 
 /// A `Key` in the DHT keyspace with preserved preimage.
@@ -193,7 +193,7 @@ impl AsRef<KeyBytes> for KeyBytes {
 
 /// A distance between two keys in the DHT keyspace.
 #[derive(Copy, Clone, PartialEq, Eq, Default, PartialOrd, Ord, Debug)]
-pub struct Distance(pub(super) U256);
+pub struct Distance(pub U256);
 
 impl Distance {
     /// Returns the integer part of the base 2 logarithm of the [`Distance`].

protocols/kad/src/lib.rs

@@ -67,7 +67,7 @@ pub use behaviour::{
     QueryResult, QueryStats, Quorum, RoutingUpdate, StoreInserts,
 };
 pub use kbucket::{
-    Distance as KBucketDistance, EntryView, KBucketRef, Key as KBucketKey, NodeStatus,
+    Distance as KBucketDistance, EntryView, KBucketRef, Key as KBucketKey, NodeStatus, U256,
 };
 use libp2p_swarm::StreamProtocol;
 pub use protocol::{ConnectionType, KadPeer};