feat: add support for batched JSON-RPC requests

[lpahlavi]

(DEFI-2565) Add support for JSON-RPC batch requests and responses. This mostly involves implementing existing JSON-RPC middlewares for JSON-RPC batches in addition to JSON-RPC single requests.

[lpahlavi]

@gregorydemay I did quite a bit of experimenting here with different solutions to make this as easy to use as possible despite all the generics involved with tower middlewares. For example I considered an enum wrapping single requests and batch requests, some traits for request/response pairs that are valid JSON-RPC calls (i.e. HttpJsonRpcRequest/HttpJsonRpcResponse and HttpBatchJsonRpcRequest/HttpBatchJsonRpcResponse), etc. In the end I think things as they are now are a pretty good tradeoff between being generic and usable, but let me know if you have any specific ideas/concerns and I can let you know why I didn't go in those directions.