2.1 - Implement Zcash RPC functionality required by lightwallet services, backed by Zebra's ReadStateService

[idky137]

Integrate with Zebra's ReadStateService to access the finalised and non-finalised chain. This should be implemented in Zaino-State to be accessible as a standalone library. Integration with TrustedChainSync for accessing the non-finalised state should be encapsulated, requiring no user-side setup.

Implement RPC functionality required by lightwallet RPC services backed by Zebra's ReadStateService, keeping backwards compatibility options where possible.

• Blocked on 1.3 Convert Indexer service to use zebra’s primitives. #50, 1.4 - Implement test framework showing equivalence between legacy and new implementation. #51
• Task 2.1.5 Blocked on Upgrade Zaino-testutils to use zcash-local-net. #96

Tasks

• Task 2.1.1: Create StateService struct in Zaino-State, initially containing Zebra's ReadStateService, and implement sync method (using Zebra's TrustedChainSync) as a persistent background process.
• Task 2.1.2: Implement Zcash RPC functionality required by lightwallet services.
• Task 2.1.3: Add Indexer Trait.
• Task 2.1.4: Implement Indexer for StateService
• Task 2.1.5: Add tests for Zcash RPC functionality backed by StateService.