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

na

testing/node_test_rig/src/lib.rs

@@ -231,7 +231,7 @@ impl<E: EthSpec> LocalExecutionNode<E> {
             .tempdir()
             .expect("should create temp directory for client datadir");
         let jwt_file_path = datadir.path().join("jwt.hex");
-        if let Err(e) = std::fs::write(&jwt_file_path, config.jwt_key.hex_string()) {
+        if let Err(e) = std::fs::write(jwt_file_path, config.jwt_key.hex_string()) {
             panic!("Failed to write jwt file {}", e);
         }
         Self {