ocaml: phase 5.1 anagram_groups.ml baseline (group by canonical anagram, 3 groups)

canonical builds a sorted-by-frequency string representation:

  let canonical s =
    let chars = Array.make 26 0 in
    for i = 0 to String.length s - 1 do
      let k = Char.code s.[i] - Char.code 'a' in
      if k >= 0 && k < 26 then chars.(k) <- chars.(k) + 1
    done;
    expand into a-z order via a Buffer

For 'eat', 'tea', 'ate' -> all canonicalise to 'aet'. For 'tan',
'nat' -> 'ant'. For 'bat' -> 'abt'.

group_anagrams folds the input, accumulating per-key string lists;
final answer is Hashtbl.length (number of distinct groups):

  ['eat'; 'tea'; 'tan'; 'ate'; 'nat'; 'bat']  -> 3 groups

99 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -2,6 +2,7 @@
   "ackermann.ml": 125,
   "adler32.ml": 300286872,
   "anagram_check.ml": 2,
+  "anagram_groups.ml": 3,
   "anagrams.ml": 3,
   "atm.ml": 120,
   "bag.ml": 3,