Add Nethermind integration tests (#3100)

## Proposed Changes

Extend the current Geth merge integration tests to support Nethermind.

testing/execution_engine_integration/src/geth.rs

@@ -0,0 +1,110 @@
+use crate::build_utils;
+use crate::execution_engine::GenericExecutionEngine;
+use crate::genesis_json::geth_genesis_json;
+use std::path::{Path, PathBuf};
+use std::process::{Child, Command, Output};
+use std::{env, fs::File};
+use tempfile::TempDir;
+use unused_port::unused_tcp_port;
+
+const GETH_BRANCH: &str = "merge-kiln-v2";
+const GETH_REPO_URL: &str = "https://github.com/MariusVanDerWijden/go-ethereum";
+
+pub fn build_result(repo_dir: &Path) -> Output {
+    Command::new("make")
+        .arg("geth")
+        .current_dir(&repo_dir)
+        .output()
+        .expect("failed to make geth")
+}
+
+pub fn build(execution_clients_dir: &Path) {
+    let repo_dir = execution_clients_dir.join("go-ethereum");
+
+    if !repo_dir.exists() {
+        // Clone the repo
+        assert!(build_utils::clone_repo(
+            execution_clients_dir,
+            GETH_REPO_URL
+        ));
+    }
+
+    // Checkout the correct branch
+    assert!(build_utils::checkout_branch(&repo_dir, GETH_BRANCH));
+
+    // Update the branch
+    assert!(build_utils::update_branch(&repo_dir, GETH_BRANCH));
+
+    // Build geth
+    build_utils::check_command_output(build_result(&repo_dir), "make failed");
+}
+
+/*
+ * Geth-specific Implementation for GenericExecutionEngine
+ */
+
+#[derive(Clone)]
+pub struct GethEngine;
+
+impl GethEngine {
+    fn binary_path() -> PathBuf {
+        let manifest_dir: PathBuf = env::var("CARGO_MANIFEST_DIR").unwrap().into();
+        manifest_dir
+            .join("execution_clients")
+            .join("go-ethereum")
+            .join("build")
+            .join("bin")
+            .join("geth")
+    }
+}
+
+impl GenericExecutionEngine for GethEngine {
+    fn init_datadir() -> TempDir {
+        let datadir = TempDir::new().unwrap();
+
+        let genesis_json_path = datadir.path().join("genesis.json");
+        let mut file = File::create(&genesis_json_path).unwrap();
+        let json = geth_genesis_json();
+        serde_json::to_writer(&mut file, &json).unwrap();
+
+        let output = Command::new(Self::binary_path())
+            .arg("--datadir")
+            .arg(datadir.path().to_str().unwrap())
+            .arg("init")
+            .arg(genesis_json_path.to_str().unwrap())
+            .output()
+            .expect("failed to init geth");
+
+        build_utils::check_command_output(output, "geth init failed");
+
+        datadir
+    }
+
+    fn start_client(
+        datadir: &TempDir,
+        http_port: u16,
+        http_auth_port: u16,
+        jwt_secret_path: PathBuf,
+    ) -> Child {
+        let network_port = unused_tcp_port().unwrap();
+
+        Command::new(Self::binary_path())
+            .arg("--datadir")
+            .arg(datadir.path().to_str().unwrap())
+            .arg("--http")
+            .arg("--http.api")
+            .arg("engine,eth")
+            .arg("--http.port")
+            .arg(http_port.to_string())
+            .arg("--authrpc.port")
+            .arg(http_auth_port.to_string())
+            .arg("--port")
+            .arg(network_port.to_string())
+            .arg("--authrpc.jwtsecret")
+            .arg(jwt_secret_path.as_path().to_str().unwrap())
+            .stdout(build_utils::build_stdio())
+            .stderr(build_utils::build_stdio())
+            .spawn()
+            .expect("failed to start geth")
+    }
+}