Make set_array to work with all supported data types.

`Ndarray.set_fancy*` functions unfortunately don't work for array
kinds other than Float32, Float64, Complex32 and Complex64.
See: owlbarn/owl#671 . As a workaround
we manually set each coordinate one-at-time using the basic
set function which does not suffer from this bug. It is likely
much slower for large Zarr chunks but necessary for usability.

lib/storage/storage.ml

@@ -175,19 +175,14 @@ module Make (M : STORE) : S with type t = M.t = struct
  | Error _ ->
  Ok (Ndarray.create repr.kind repr.shape repr.fill_value))
  >>= fun arr ->
- (* find_all returns bindings in reverse order. To restore the
- * C-ordering of elements we must call List.rev. *)
- let coords, vals =
- List.split @@
- List.rev @@
- Arraytbl.find_all tbl idx in
- let slice' = Indexing.slice_of_coords coords in
- let shape' = Indexing.slice_shape slice' repr.shape in
- let x' = Ndarray.of_array repr.kind (Array.of_list vals) shape' in
- (* Ndarray.set_fancy* unfortunately doesn't work for array kinds
- other than Float32, Float64, Complex32 and Complex64.
- See: https://github.com/owlbarn/owl/issues/671 *)
- Ndarray.set_fancy_ext slice' arr x'; (* possible to rewrite this function? *)
+ (* NOTE: Ndarray.set_fancy* functions unfortunately don't work for array
+ kinds other than Float32, Float64, Complex32 and Complex64.
+ See: https://github.com/owlbarn/owl/issues/671 . As a workaround
+ we manually set each coordinate one-at-time using the basic
+ set function which does not suffer from this bug. It is likely
+ much slower for large Zarr chunks but necessary for usability.*)
+ List.iter
+ (fun (c, v) -> Ndarray.set arr c v) @@ Arraytbl.find_all tbl idx;
  Codecs.Chain.encode codecs arr >>| fun encoded ->
  set t chunkkey encoded) cindices (Ok ())