Replace `QCheck` unit tests with `Quickcheck`

Dromedary's current testing framework relies on `Alcotest`, `QCheck` and Jane Street's Expect Tests.
This issue aims to remove `QCheck` by using Jane Street's `Quickcheck` library:
```ocaml
module T = struct
  type t = 
    | ...
  [@@deriving quickcheck]
end

let%test_unit = 
  Quickcheck.run T.quickcheck_generator ~f:(fun t -> ...)
```