ocaml: phase 5.1 subseq_check.ml baseline (subsequence test, 3/5 yes)

Two-pointer walk:

  let is_subseq s t =
    let i = ref 0 in
    let j = ref 0 in
    while !i < n && !j < m do
      if s.[!i] = t.[!j] then i := !i + 1;
      j := !j + 1
    done;
    !i = n

advance i only on match; always advance j. Pattern matches if i
reaches n.

Five test cases:
  'abc'  in 'ahbgdc'    yes
  'axc'  in 'ahbgdc'    no  (no x in t)
  ''     in 'anything'  yes (empty trivially)
  'abc'  in 'abc'       yes
  'abcd' in 'abc'       no  (s longer)
  sum = 3

93 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -79,6 +79,7 @@
   "shuffle.ml": 55,
   "simpson_int.ml": 10000,
   "stable_unique.ml": 46,
+  "subseq_check.ml": 3,
   "subset_sum.ml": 8,
   "tic_tac_toe.ml": 1,
   "word_freq.ml": 8,