feature: Remote ReadStateService.

[idky137]

Motivation

Zebra’s ReadStateService currently only allows local access, limiting its integration with external tools and remote debugging. Enabling remote access would streamline workflows, simplify testing, and support scalable, decentralized deployments—fostering a more modular and community-friendly Zcash ecosystem

This feature was discussed in several Zcashd deprecation meetings and it was agreed that the Zaino dev team would take responsibility for implementing this functionality.

Specifications

The current plan for this feature is as follows:

1. Use Serde to implement Serialize and Deserialize for the ReadRequest and ReadResponse structs in Zebra-State.
   *This step will also require changes in librustzcash::zcash_history. (Add Serde Serialize and Deserialise to structs in zcash_history zcash/librustzcash#1744)

2. Add a remote_state_request RPC to Zebra's JsonRPC server that acts as a wrapper to the ReadStateService's Call method.

3. Add a RemoteStateService to zebra-state::service that uses JsonRpSee to send state requests to Zebrad and implement tower::Service for equivalent functionality. (Could be implemented in Zaino?)

NOTE: The current plan is to add this feature under a "remote_read_state_service" feature flag but this could be removed if this functionality should be enabled by default.

Complex Code or Requirements

NA

Testing

Possible solution: Add set of tests that compare output of Call method from both ReadStateService and RemoteStateService.

Related Work

NA

[idky137]

zcash/librustzcash#1745 is the first work towards this feature and is now waiting for review in librustzcash.