soroban-rpc: add jrpc2 batch compliance test

[tsachiherman]

What

add jrpc2 batch compliance test

Why

Add a test to verify the output of the jrpc library.

Known limitations

n/a

[2opremio]

Doesn't this belong to the library itself?

[tsachiherman]

Doesn't this belong to the library itself?

Yes.. but I wanted to confirm that on our end first.

I agree that this test need to move to the library.

[tsachiherman]

I spent some time looking into this issue. According to the jrpc2 specification:

	//
	//   The Server SHOULD respond with an Array containing the corresponding
	//   Response objects
	//

where the word SHOULD is interpreted as per RPC 2119:

3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

which means that the responsibility for decoding this either as an array or a single element falls on the client, which MUST be capable of supporting both, given that it knows that the server has that flexibility.

Would I implement it in that way ? most likely not. But any client being unable to decode the response is a non-compliant client, whereas the server is protocol compliant.