ocaml: phase 5.1 rolling_hash.ml baseline (Rabin-Karp, 6 "abc" matches)

Polynomial rolling hash mod 1000003 with base 257:
  - precompute base^(m-1)
  - slide window updating hash in O(1) per step
  - verify hash match with O(m) memcmp to skip false positives

  rolling_match "abcabcabcabcabcabc" "abc" = 6

Six non-overlapping copies of "abc" at positions 0,3,6,9,12,15.

Tests `for _ = 0 to m - 2 do … done` unused loop variable
(uses underscore wildcard pattern), Char.code arithmetic, mod
arithmetic with intermediate negative subtractions, complex nested
if/begin branching with inner break-via-flag.

151 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -122,6 +122,7 @@
   "quickselect.ml": 5,
   "quicksort.ml": 44,
   "roman.ml": 44,
+  "rolling_hash.ml": 6,
   "reverse_int.ml": 54329,
   "rpn.ml": 9,
   "run_decode.ml": 21,