split doesn't handle modified ranges

[aldrikfr]

Describe the bug
if split is called on a modified range, split actually ignores the modifiers

To Reproduce

utop # Range.(from 1 5000 |> map ~f:((+) 3)  |> Number.(split (gtz_from_int_exn 100) (gtz_from_int_exn 24)) |> List.map to_string);;
- : string list =
["Nat:4808:5000"; "Nat:4599:4807"; "Nat:4390:4598"; "Nat:4181:4389";
 "Nat:3972:4180"; "Nat:3763:3971"; "Nat:3554:3762"; "Nat:3345:3553";
 "Nat:3136:3344"; "Nat:2927:3135"; "Nat:2718:2926"; "Nat:2509:2717";
 "Nat:2300:2508"; "Nat:2091:2299"; "Nat:1882:2090"; "Nat:1673:1881";
 "Nat:1464:1672"; "Nat:1255:1463"; "Nat:1046:1254"; "Nat:837:1045";
 "Nat:628:836"; "Nat:419:627"; "Nat:210:418"; "Nat:1:209"]

Expected behavior
The same result plus 3; and with de mod flag instead of Nat

[aldrikfr]

Only the modifier flag in the case of the example