Add Hash trait to Selector struct (#2149)

* Add Hash trait to Selector struct

* Update changelog

* Make Hash derive conditional

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+- Add Hash trait to Selector struct
 
 ## Version 5.0.0-rc.3
 

crates/metadata/src/specs.rs

@@ -52,7 +52,10 @@ use serde::{
     Serialize,
 };
 #[cfg(feature = "std")]
-use std::collections::BTreeMap;
+use std::{
+    collections::BTreeMap,
+    hash::Hash,
+};
 
 /// Describes a contract.
 #[derive(Debug, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
@@ -1091,6 +1094,7 @@ where
 }
 
 /// The 4 byte selector to identify constructors and messages
+#[cfg_attr(feature = "std", derive(Hash))]
 #[derive(Debug, Default, PartialEq, Eq, derive_more::From, JsonSchema)]
 pub struct Selector(#[schemars(with = "String")] [u8; 4]);