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/baseline/expected.json

@@ -8,6 +8,7 @@
   "exception_handle.ml": 4,
   "expr_eval.ml": 16,
   "factorial.ml": 3628800,
+  "frequency.ml": 5,
   "fizzbuzz.ml": 57,
   "list_ops.ml": 30,
   "lambda_calc.ml": 7,