Engine API v1.0.0.alpha.6 + interop tests (#3024)

## Issue Addressed

NA

## Proposed Changes

This PR extends #3018 to address my review comments there and add automated integration tests with Geth (and other implementations, in the future).

I've also de-duplicated the "unused port" logic by creating an  `common/unused_port` crate.

## Additional Info

I'm not sure if we want to merge this PR, or update #3018 and merge that. I don't mind, I'm primarily opening this PR to make sure CI works.


Co-authored-by: Mark Mackey <mark@sigmaprime.io>

Cargo.lock

@@ -361,6 +361,7 @@ dependencies = [
  "store",
  "task_executor",
  "types",
+ "unused_port",
 ]
 
 [[package]]
@@ -626,9 +627,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.0.72"
+version = "1.0.73"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "22a9137b95ea06864e018375b72adfb7db6e6f68cfc8df5a04d00288050485ee"
+checksum = "2fff2a6927b3bb87f9595d67196a70493f627687a71d87a0d692242c33f58c11"
 
 [[package]]
 name = "cexpr"
@@ -1499,6 +1500,7 @@ dependencies = [
  "serde_json",
  "tokio",
  "types",
+ "unused_port",
  "web3",
 ]
 
@@ -1804,6 +1806,23 @@ dependencies = [
  "uint 0.9.3",
 ]
 
+[[package]]
+name = "execution_engine_integration"
+version = "0.1.0"
+dependencies = [
+ "environment",
+ "execution_layer",
+ "exit-future",
+ "futures",
+ "sensitive_url",
+ "serde_json",
+ "task_executor",
+ "tempfile",
+ "tokio",
+ "types",
+ "unused_port",
+]
+
 [[package]]
 name = "execution_layer"
 version = "0.1.0"
@@ -3325,6 +3344,7 @@ dependencies = [
  "task_executor",
  "tempfile",
  "types",
+ "unused_port",
  "validator_client",
  "validator_dir",
 ]
@@ -3380,6 +3400,7 @@ dependencies = [
  "tokio-util",
  "types",
  "unsigned-varint 0.6.0",
+ "unused_port",
  "void",
 ]
 
@@ -6599,6 +6620,10 @@ version = "0.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a156c684c91ea7d62626509bce3cb4e1d9ed5c4d978f7b4352658f96a4c26b4a"
 
+[[package]]
+name = "unused_port"
+version = "0.1.0"
+
 [[package]]
 name = "url"
 version = "2.2.2"