Make socket listener tests more readable. (valkey-io#1027)

* Move socket reading into response assert.

This removes reading from socket before asserting on the read value from multiple tests.

* Add helper function to assert on values.

* Remove unused cursor argument.

* Move repeating read logic to function.

* Increase setup legibility.

2-3 booleans in a row are hard to read without confusion. Using enums instead.

* Move repeated writing logic to write helpers.

* Add pointer to value helper function.

* Add another writer helper method.

* fix comments