Clippy lints for rust 1.66 (#3810)

## Issue Addressed
Fixes the new clippy lints for rust 1.66

## Proposed Changes

Most of the changes come from:
- [unnecessary_cast](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast)
- [iter_kv_map](https://rust-lang.github.io/rust-clippy/master/index.html#iter_kv_map)
- [needless_borrow](https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow)

## Additional Info

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consensus/serde_utils/src/hex.rs

@@ -63,15 +63,15 @@ mod test {
     #[test]
     fn encoding() {
         let bytes = vec![0, 255];
-        let hex = encode(&bytes);
+        let hex = encode(bytes);
         assert_eq!(hex.as_str(), "0x00ff");
 
         let bytes = vec![];
-        let hex = encode(&bytes);
+        let hex = encode(bytes);
         assert_eq!(hex.as_str(), "0x");
 
         let bytes = vec![1, 2, 3];
-        let hex = encode(&bytes);
+        let hex = encode(bytes);
         assert_eq!(hex.as_str(), "0x010203");
     }
 }

consensus/serde_utils/src/u64_hex_be.rs

@@ -36,7 +36,7 @@ impl<'de> Visitor<'de> for QuantityVisitor {
         } else if stripped.starts_with('0') {
             Err(de::Error::custom("cannot have leading zero"))
         } else if stripped.len() % 2 != 0 {
-            hex::decode(&format!("0{}", stripped))
+            hex::decode(format!("0{}", stripped))
                 .map_err(|e| de::Error::custom(format!("invalid hex ({:?})", e)))
         } else {
             hex::decode(stripped).map_err(|e| de::Error::custom(format!("invalid hex ({:?})", e)))