Relaxed clippy fixes/nits (#2661)

This PR contains just a few clippy fixes and nits, which are, however,
relaxed by workspace clippy settings here:
https://github.com/paritytech/polkadot-sdk/blob/master/Cargo.toml#L483-L506

---------

Co-authored-by: Dmitry Sinyavin <dmitry.sinyavin@parity.io>
Co-authored-by: ordian <write@reusable.software>
Co-authored-by: command-bot <>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/primitives/storage/src/lib.rs

@@ -414,12 +414,13 @@ impl ChildTrieParentKeyId {
 ///
 /// V0 and V1 uses a same trie implementation, but V1 will write external value node in the trie for
 /// value with size at least `TRIE_VALUE_NODE_THRESHOLD`.
-#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+#[derive(Debug, Default, Clone, Copy, Eq, PartialEq)]
 #[cfg_attr(feature = "std", derive(Encode, Decode))]
 pub enum StateVersion {
 	/// Old state version, no value nodes.
 	V0 = 0,
 	/// New state version can use value nodes.
+	#[default]
 	V1 = 1,
 }
 
@@ -432,12 +433,6 @@ impl Display for StateVersion {
 	}
 }
 
-impl Default for StateVersion {
-	fn default() -> Self {
-		StateVersion::V1
-	}
-}
-
 impl From<StateVersion> for u8 {
 	fn from(version: StateVersion) -> u8 {
 		version as u8