ocaml: phase 5.1 flood_fill.ml baseline (largest grid component = 7)

Recursive 4-way flood fill from every unvisited 1-cell:

  let rec flood visited r c =
    if r < 0 || r >= h || c < 0 || c >= w then 0
    else if visited.(r).(c) || grid.(r).(c) = 0 then 0
    else begin
      visited.(r).(c) <- true;
      1 + flood visited (r - 1) c
        + flood visited (r + 1) c
        + flood visited r (c - 1)
        + flood visited r (c + 1)
    end

Grid (1s shown as #, 0s as .):
  # # . # #
  # . . . #
  . . # . .
  # # # # .
  . . . # #

Largest component: {(2,2),(3,0),(3,1),(3,2),(3,3),(4,3),(4,4)} = 7.

Bounds check r >= 0 must short-circuit before visited/grid reads;
relies on the && / || fix from iter 242.

157 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -73,6 +73,7 @@
   "fizz_classifier.ml": 540,
   "fizzbuzz.ml": 57,
   "flatten_tree.ml": 28,
+  "flood_fill.ml": 7,
   "floyd_warshall.ml": 9,
   "lis.ml": 6,
   "list_ops.ml": 30,