Add cluster slots parsing tests

[bjosv]

Adds CLUSTER SLOTS parser tests, which uses a testsuite-local primitive parser of a JSON subset to encode arrays to RESP.

[zuiderkwast]

Interesting! I guess it's pretty easy to convert this pseudo-JSON to RESP, althought it adds some non-trivial code to the testing. My first though is that single-quoted stings are not allowed in JSON. :)

My second thought is that it might be possible to construct a parse tree structure that is readable and easy to serialize to RESP, without parsing. Ideally, test code should be trivial, so there is no doubt if there's a bug, is it a bug in the test code or in the real implementation?

Here is a reply literal with the first slot range (untested). It's much bigger than the pseudo-JSON obviously.

valkeyReply reply = {.type = VALKEY_REPLY_ARRAY, .elements = 3, .element = (valkeyReply[]){
    {.type = VALKEY_REPLY_ARRAY, .elements = 4, .element = (valkeyReply[]){
        {.type = VALKEY_REPLY_INTEGER, .integer = 0},
        {.type = VALKEY_REPLY_INTEGER, .integer = 5460},
        {.type = VALKEY_REPLY_ARRAY, .elements = 4, .element = (valkeyReply[]){
            {.type = VALKEY_REPLY_STRING, .str = "127.0.0.1"},
            {.type = VALKEY_REPLY_INTEGER, .integer = 30005},
            {.type = VALKEY_REPLY_STRING, .str = "e7d1eecce10fd6bb5eb35b9f99a514335d9ba9ca"},
            {.type = VALKEY_REPLY_ARRAY, .elements = 2, .element = (valkeyReply[]){
                {.type = VALKEY_REPLY_STRING, .str = "hostname"},
                {.type = VALKEY_REPLY_STRING, .str = "localhost"} 
            }
        }
    },
    ...
};