ocaml: phase 5.1 task_scheduler.ml baseline ("AAABBC" cooldown 2 -> 7)

Task-scheduler closed-form min total intervals:

  m = max letter frequency
  k = number of letters tied at frequency m
  answer = max((m - 1) * (n + 1) + k, total_tasks)

For "AAABBC" with cooldown n = 2:
  freq A = 3, freq B = 2, freq C = 1 -> m = 3, k = 1
  formula = (3 - 1) * (2 + 1) + 1 = 7
  total tasks = 6
  answer = 7

Witness schedule: A, B, C, A, B, idle, A.

Tests String.iter with side-effecting count update via
Char.code arithmetic, fixed-size 26-bucket histogram.

195 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -173,6 +173,7 @@
   "stock_two.ml": 6,
   "subseq_check.ml": 3,
   "tail_factorial.ml": 479001600,
+  "task_scheduler.ml": 7,
   "tarjan_scc.ml": 4,
   "subset_sum.ml": 8,
   "tic_tac_toe.ml": 1,