jsonrpsee supports three different types on calls sync, async and blocking

The methods has just been ported how they were defined via https://github.com/paritytech/jsonrpc so just sync or async but some RPC calls that are sync I/O such as reading DB might facilitate from using tokio::spawn_blocking instead of tokio::spawn which is used for the calls defined as async RPC calls.

See paritytech/jsonrpsee#486 for further information