Fix encoding/decoding of arrays of domains defined over arrays

[greg-rychlewski]

Sorry for throwing another weird one your way about domains. This comment here basically explains it

# A nested array is normally handled by recursing through the dimensions
  # until you hit the base element. However, there is a special case
  # where a parameter may look like a nested array but we cannot treat it
  # this way. An array whose element type is a domain that is defined
  # over an array will look like a nested array from Elixir, but the
  # Postgres protocol must treat it as a single dimensional array over
  # the domain type

[greg-rychlewski]

The reason why this check works is because no matter how many dimensions the array is over a non-domain type, the sub type is still considered the base type. For example [[[[[int]]]]] will still just have a sub type of int. This is enforced by Postgres and not just a quirk of how we handle types.

But [domain_over_array] will have a sub type of array. This is also enforced by postgres or else the protocol rejects it. i.e. postgres doesn't see base_type[][] the same as domain_over_array_of_base_type[].