ocaml: phase 4 Set.Make / Map.Make functor application smoke tests (+3 tests, 572 total)

Functors were already wired through ocaml-make-functor in eval.sx
(curried host closure consuming module dicts) but had no explicit
tests for the user-defined Ord application path. This commit adds
three smoke tests that confirm:

  module IntOrd = struct let compare a b = a - b end
  module S = Set.Make (IntOrd)

  S.elements (fold-add [5;1;3;1;5])    sums to 9 (dedupe + sort)
  S.mem 2 (S.add 1 (S.add 2 (S.add 3 S.empty)))   = true
  M.cardinal (M.add 1 'a' (M.add 2 'b' M.empty))  = 2

The Ord parameter is properly threaded through the functor body —
elements are sorted in compare order and dedupe works.

plans/ocaml-on-sx.md

@@ -407,6 +407,13 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-09 Phase 4 — Set.Make / Map.Make functor application
+  smoke tests (+3 tests, 572 total). Functors were already wired
+  through ocaml-make-functor in eval.sx but had no explicit tests
+  for the user-defined Ord application path. Confirms that
+  `module S = Set.Make (IntOrd) ;; let s = ... in S.elements s`,
+  `S.mem 2 s`, and `Map.Make (IntOrd) ;; M.cardinal m` all work end
+  to end.
 - 2026-05-09 Phase 6 — Filename module + Char.compare/equal/escaped
   (+7 tests, 569 total). Filename: basename, dirname, extension,
   chop_extension, concat, is_relative + dir_sep / current_dir_name /