ocaml: phase 5.1 group_consec.ml baseline (group consecutive equals, 5*10+3 = 53)

Inner 'collect cur acc tail' walks the tail while head matches
'cur', accumulating into 'acc'. Returns (rev acc, remaining) on
first mismatch. Outer 'group' recurses on the remaining list.

  group [1;1;2;2;2;3;1;1;4]
   = [[1;1]; [2;2;2]; [3]; [1;1]; [4]]

  List.length groups        = 5
  List.length (gs.(1))      = 3
  5 * 10 + 3                = 53

Tests nested recursion (inner aux + outer recursion), tuple
destructuring 'let (g, tail) = ...' inside the outer match arm,
and List.nth.

69 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -28,6 +28,7 @@
   "frequency.ml": 5,
   "gcd_lcm.ml": 60,
   "grep_count.ml": 3,
+  "group_consec.ml": 53,
   "hailstone.ml": 111,
   "hanoi.ml": 1023,
   "fizzbuzz.ml": 57,