ocaml: phase 5 HM ctor inference for option/result (+7 tests, 351 total)

ocaml-hm-ctor-env registers None/Some : 'a -> 'a option, Ok/Error :
'a -> ('a, 'b) result. :con NAME instantiates the scheme; :pcon NAME
ARG-PATS walks arg patterns through the constructor's arrow type,
unifying each.

Pretty-printer renders 'Int option' and '(Int, 'b) result'.

Examples now infer:
  fun x -> Some x : 'a -> 'a option
  match Some 5 with | None -> 0 | Some n -> n : Int
  fun o -> match o with | None -> 0 | Some n -> n : Int option -> Int
  Ok 1 : (Int, 'b) result
  Error "oops" : ('a, String) result

User type-defs would extend the registry — pending.

lib/ocaml/test.sh

@@ -856,6 +856,22 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1804)
 (eval "(ocaml-type-of \"fun lst -> match lst with | [] -> 0 | h :: _ -> h\")")
 
+;; ── HM constructor inference (option/result) ───────────────────
+(epoch 1900)
+(eval "(ocaml-type-of \"Some 5\")")
+(epoch 1901)
+(eval "(ocaml-type-of \"None\")")
+(epoch 1902)
+(eval "(ocaml-type-of \"Ok 1\")")
+(epoch 1903)
+(eval "(ocaml-type-of \"Error \\\"oops\\\"\")")
+(epoch 1904)
+(eval "(ocaml-type-of \"fun x -> Some x\")")
+(epoch 1905)
+(eval "(ocaml-type-of \"match Some 5 with | None -> 0 | Some n -> n\")")
+(epoch 1906)
+(eval "(ocaml-type-of \"fun o -> match o with | None -> 0 | Some n -> n\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1354,6 +1370,15 @@ check 1802 "match tuple"                  '"Int"'
 check 1803 "fn match int -> int"          '"Int -> Int"'
 check 1804 "fn list -> elem"              '"Int list -> Int"'
 
+# ── HM ctor inference ──────────────────────────────────────────
+check 1900 "Some 5 : Int option"          '"Int option"'
+check 1901 "None : 'a option"             ' option'
+check 1902 "Ok 1 : (Int, 'b) result"      '"(Int'
+check 1903 "Error 'oops'"                 'String) result'
+check 1904 "fun x -> Some x"              ' option'
+check 1905 "match Some/None -> Int"       '"Int"'
+check 1906 "Int option -> Int"            '"Int option -> Int"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"