Rename random to prev_randao (#3040)

## Issue Addressed

As discussed on last-night's consensus call, the testnets next week will target the [Kiln Spec v2](https://hackmd.io/@n0ble/kiln-spec).

Presently, we support Kiln V1. V2 is backwards compatible, except for renaming `random` to `prev_randao` in:

- https://github.com/ethereum/execution-apis/pull/180
- https://github.com/ethereum/consensus-specs/pull/2835

With this PR we'll no longer be compatible with the existing Kintsugi and Kiln testnets, however we'll be ready for the testnets next week. I raised this breaking change in the call last night, we are all keen to move forward and break things.

We now target the [`merge-kiln-v2`](https://github.com/MariusVanDerWijden/go-ethereum/tree/merge-kiln-v2) branch for interop with Geth. This required adding the `--http.aauthport` to the tester to avoid a port conflict at startup.

### Changes to exec integration tests

There's some change in the `merge-kiln-v2` version of Geth that means it can't compile on a vanilla Github runner. Bumping the `go` version on the runner solved this issue.

Whilst addressing this, I refactored the `testing/execution_integration` crate to be a *binary* rather than a *library* with tests. This means that we don't need to run the `build.rs` and build Geth whenever someone runs `make lint` or `make test-release`. This is nice for everyday users, but it's also nice for CI so that we can have a specific runner for these tests and we don't need to ensure *all* runners support everything required to build all execution clients.

## More Info

- [x] ~~EF tests are failing since the rename has broken some tests that reference the old field name. I have been told there will be new tests released in the coming days (25/02/22 or 26/02/22).~~

testing/execution_engine_integration/src/execution_engine.rs

@@ -9,7 +9,7 @@ use unused_port::unused_tcp_port;
 /// Defined for each EE type (e.g., Geth, Nethermind, etc).
 pub trait GenericExecutionEngine: Clone {
     fn init_datadir() -> TempDir;
-    fn start_client(datadir: &TempDir, http_port: u16) -> Child;
+    fn start_client(datadir: &TempDir, http_port: u16, http_auth_port: u16) -> Child;
 }
 
 /// Holds handle to a running EE process, plus some other metadata.
@@ -19,6 +19,7 @@ pub struct ExecutionEngine<E> {
     #[allow(dead_code)]
     datadir: TempDir,
     http_port: u16,
+    http_auth_port: u16,
     child: Child,
 }
 
@@ -35,11 +36,13 @@ impl<E: GenericExecutionEngine> ExecutionEngine<E> {
     pub fn new(engine: E) -> Self {
         let datadir = E::init_datadir();
         let http_port = unused_tcp_port().unwrap();
-        let child = E::start_client(&datadir, http_port);
+        let http_auth_port = unused_tcp_port().unwrap();
+        let child = E::start_client(&datadir, http_port, http_auth_port);
         Self {
             engine,
             datadir,
             http_port,
+            http_auth_port,
             child,
         }
     }
@@ -47,6 +50,11 @@ impl<E: GenericExecutionEngine> ExecutionEngine<E> {
     pub fn http_url(&self) -> SensitiveUrl {
         SensitiveUrl::parse(&format!("http://127.0.0.1:{}", self.http_port)).unwrap()
     }
+
+    #[allow(dead_code)] // Future use.
+    pub fn http_ath_url(&self) -> SensitiveUrl {
+        SensitiveUrl::parse(&format!("http://127.0.0.1:{}", self.http_auth_port)).unwrap()
+    }
 }
 
 /*
@@ -90,7 +98,7 @@ impl GenericExecutionEngine for Geth {
         datadir
     }
 
-    fn start_client(datadir: &TempDir, http_port: u16) -> Child {
+    fn start_client(datadir: &TempDir, http_port: u16, http_auth_port: u16) -> Child {
         let network_port = unused_tcp_port().unwrap();
 
         Command::new(Self::binary_path())
@@ -101,6 +109,8 @@ impl GenericExecutionEngine for Geth {
             .arg("engine,eth")
             .arg("--http.port")
             .arg(http_port.to_string())
+            .arg("--http.authport")
+            .arg(http_auth_port.to_string())
             .arg("--port")
             .arg(network_port.to_string())
             .stdout(build_stdio())