feat: real sr25519 signatures + binary evaluation in Docker

- validator-node: Replace placeholder signatures with real sr25519 signing
- validator-node: Listen for binary_ready event instead of new_submission_assigned
- validator-node: Implement full binary evaluation flow in isolated Docker container
- validator-node: Add BinaryReadyPayload struct for new event type
- Cargo.toml: Add tempfile dependency for binary evaluation

Author: echobt

Cargo.lock

@@ -50,3 +50,6 @@ uuid = { version = "1.0", features = ["v5"] }
 tokio-tungstenite = { version = "0.21", features = ["native-tls"] }
 futures-util = "0.3"
 url = "2.5"
+
+# Binary evaluation
+tempfile = "3.10"