*: Apply clippy suggestions and enable clippy on CI (#1850)

* *: Apply clippy suggestions

* .github: Add clippy check

* protocols/kad/record: Implement custom PartialEq for ProviderRecord

misc/multiaddr/src/lib.rs

@@ -40,6 +40,7 @@ static_assertions::const_assert! {
 }
 
 /// Representation of a Multiaddr.
+#[allow(clippy::rc_buffer)]
 #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
 pub struct Multiaddr { bytes: Arc<Vec<u8>> }
 
@@ -59,6 +60,11 @@ impl Multiaddr {
         self.bytes.len()
     }
 
+    /// Returns true if the length of this multiaddress is 0.
+    pub fn is_empty(&self) -> bool {
+        self.bytes.len() == 0
+    }
+
     /// Return a copy of this [`Multiaddr`]'s byte representation.
     pub fn to_vec(&self) -> Vec<u8> {
         Vec::from(&self.bytes[..])