Prefer `array?` rather than `array`

Happy New Year! :tada: :sheep:

`array` can only be called to check to dump the `:array` option in the AR internal, therefore it is not necessary to determine until it is called. Do not remove `[]` from `sql_type` for the `array?` method. Lookup the `cast_type` from `sql_type` required `[]` also. It was not necessary to remove `[]`.
I don't think we should change the result of `Column#sql_type` without a good reason to.