ocaml: phase 5.1 bracket_match.ml baseline (5/9 balanced strings)

Stack-based multi-bracket parenthesis matching for ( [ { ) ] }.
Non-bracket chars are skipped (treated as content).

Tests:
  ()           yes
  [{()}]       yes
  ({[}])       no  (mismatched closer)
  ""           yes
  ((           no  (unclosed)
  ()[](){}     yes
  (a(b)c)      yes  (a/b/c skipped)
  (()          no
  ])           no
                 5 balanced

Body uses begin/end-wrapped match inside while:

  else if c = ')' || c = ']' || c = '}' then begin
    match !stack with
    | [] -> ok := false
    | top :: rest ->
      let pair =
        (c = ')' && top = '(') ||
        (c = ']' && top = '[') ||
        (c = '}' && top = '{')
      in
      if pair then stack := rest else ok := false
  end

Tests side-effecting match arms inside while body, ref-of-list as
stack, multi-char pairing dispatch.

174 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -15,6 +15,7 @@
   "bipartite.ml": 4,
   "bits.ml": 21,
   "balance.ml": 3,
+  "bracket_match.ml": 5,
   "base_n.ml": 17,
   "bfs.ml": 6,
   "bfs_grid.ml": 8,