db: temporal KV client index_range API via gRPC

[canepat]

This PR implements temporal KV index_range API in gRPC client. The following interface changes become necessary:

• first of all, the declaration of such API must be moved from api::Service to api::Transaction, as the input api::IndexRangeQuery always needs to specify the tx_id, i.e. the unique identifier of the enclosing db transaction
• then, the return type becomes api::PaginatedTimestamps, which is a sequence of timestamps paginated by using the api::PaginatedSequence<T> abstraction introduced in db: paginated sequence for temporal KV API #2186

Extras

• cmd: add kv_index_range command in grpc_toolbox to allow testing IndexRange KV RPC wrt Erigon3
• infra: relax parameter type from std::unique_ptr<Stub>& to Stub& in unary_rpc function to allow easy usage of ::remote::MockKVStub in unit tests
• infra: add utility function translating ::grpc::StatusCode into boost::system::error_code
• infra: add utility functions to produce gRPC status codes in unit tests
• rpc: refactor engine_api_test module to use DummyTransaction test utility