ocaml: phase 5.1 min_subarr_target.ml baseline (min subarray sum >= 7 = 2)

Classic two-pointer / sliding window: expand right, then shrink
left while the window still satisfies the >= constraint, recording
the smallest valid length.

  for r = 0 to n - 1 do
    sum := !sum + arr.(r);
    while !sum >= target do
      ... record (r - !l + 1) if smaller ...
      sum := !sum - arr.(!l);
      l := !l + 1
    done
  done

For [2; 3; 1; 2; 4; 3], target 7 -> window [4, 3] of length 2.

Sentinel n+1 marks "not found"; final guard reduces to 0.

Tests for + inner while shrinking loop, ref-tracked sum updated
on both expansion and contraction.

194 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -125,6 +125,7 @@
   "merge_sort.ml": 44,
   "merge_two.ml": 441,
   "min_cost_path.ml": 12,
+  "min_subarr_target.ml": 2,
   "module_use.ml": 3,
   "monotonic.ml": 4,
   "newton_sqrt.ml": 1414,