Review json-rpc 2.0 implementation in request_handler.cpp

[elmato]

In particular the supported types for id

spec:

id
An identifier established by the Client that MUST contain a String, Number, or NULL value if included. If it is not included it is assumed to be a notification. The value SHOULD normally not be Null [1] and Numbers SHOULD NOT contain fractional parts [2]

And the handling of invalid individual request inside a batch operation

[stephen-diesel]

We should evaluate if the latest upstream Silkworm updates fix this issue. If not resolved, this will be managed as a lower priority.