ocaml: phase 5.1 frequency.ml baseline + Format module alias (+2 tests, 498 total)

frequency.ml exercises the recently-added Hashtbl.iter / fold +
Hashtbl.find_opt + s.[i] indexing + for-loop together: build a
char-count table for 'abracadabra' then take the max via
Hashtbl.fold. Expected = 5 (a x 5). Total 25 baseline programs.

Format module added as a thin alias of Printf — sprintf, printf, and
asprintf all delegate to Printf.sprintf. The dynamic runtime doesn't
distinguish boxes/breaks, so format strings work the same as in
Printf and most Format-using OCaml programs now compile.

lib/ocaml/test.sh

@@ -1234,6 +1234,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 4961)
 (eval "(ocaml-run \"let counter = ref 0 in let lz = lazy (counter := !counter + 1; 42) in let a = Lazy.force lz in let b = Lazy.force lz in (a + b) * 100 + !counter\")")
 
+;; ── Format alias of Printf ────────────────────────────────────
+(epoch 4970)
+(eval "(ocaml-run \"Format.sprintf \\\"%d\\\" 99\")")
+(epoch 4971)
+(eval "(ocaml-run \"Format.asprintf \\\"%s=%d\\\" \\\"n\\\" 7\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 360 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1958,6 +1964,10 @@ check 4951 "Hashtbl.iter ref accum 10+20" '30'
 check 4960 "lazy 1+2 force"               '3'
 check 4961 "lazy memoization counter=1"   '8401'
 
+# ── Format alias ─────────────────────────────────────────────────
+check 4970 "Format.sprintf %d"            '"99"'
+check 4971 "Format.asprintf %s=%d"        '"n=7"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"