feat(pubsub): track eth_unsubscribe via unique request id and in-flight manager

[Galoretka]

• Generate unique Id::String from the subscription’s local id for eth_unsubscribe.
• Serialize the request, wrap in InFlight, and send via service_request to register in RequestManager.
• Prevents id collisions and ensures the unsubscribe response is consumed.
• Keeps local subscription removal semantics unchanged and remains robust across reconnects.