Epic: Queuing, caching, and load balancing

* Multiple RPC calls in parallel can overload the node
* Multiple RPC calls sequentially can be slow
* Specifying sequential/parallel complicates the API
* Implementations of some operations may consist of multiple RPC calls under the hood, depending on chain
* Some of the data does not change and can be cached indefinitely
* Some of the data can be cached until the block height increments
* The same data can be accessed through multiple RPC endpoints ran by independent parties
* RPC calls may be initiated while other RPC calls are still pending

An internal queuing/caching/load balancing mechanism could address all of the above, providing robust and performant RPC operation.