feat(coprocessor): fhevm-listener, health check

[rudy-6-4]

No description provided.

[dartdart26]

Looks good overall. I added some comments that, I think, are worth considering.

[Copilot]

Pull Request Overview

This PR introduces a health-check subsystem to the FHEVM listener, exposing liveness and readiness endpoints, and updates integration tests to validate health behavior.

• Added a new health_check module with HTTP endpoints for /liveness and /healthz.
• Integrated HealthCheck startup in main and exposed a health_port CLI flag.
• Extended integration tests to exercise the new health endpoints.

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
coprocessor/fhevm-engine/fhevm-listener/tests/integration_test.rs	Refactored DB URL constant; added test_health for health-check
coprocessor/fhevm-engine/fhevm-listener/src/lib.rs	Imported new health_check module
coprocessor/fhevm-engine/fhevm-listener/src/health_check.rs	Entire new health-check implementation
coprocessor/fhevm-engine/fhevm-listener/src/cmd/mod.rs	Added health_port arg; wired up HealthCheck in CLI handling
coprocessor/fhevm-engine/fhevm-listener/Cargo.toml	Added axum, serde_json, tokio-util, tower-http, reqwest
coprocessor/fhevm-engine/.cargo/deny.toml	Whitelisted CDLA-Permissive-2.0 license

Comments suppressed due to low confidence (2)

coprocessor/fhevm-engine/fhevm-listener/src/health_check.rs:60

• [nitpick] The status message Only connected is ambiguous; a clearer message like Connected or Health checks passed would improve readability.

        self.message = "Only connected".to_string();

coprocessor/fhevm-engine/fhevm-listener/tests/integration_test.rs:252

• The new health-check test covers only the happy path and node shutdown; consider adding tests for database-connectivity failure and blockchain-connectivity failure to exercise unhealthy branches.

#[tokio::test]