ocaml: phase 5.1 activity_select.ml baseline (greedy non-overlap = 4)

Activity selection by earliest end time. Manual bubble sort over
(start, end) tuple array, then sweep accepting whenever the next
start >= last_end.

  intervals: (1,4) (3,5) (0,6) (5,7) (3,8) (5,9) (6,10) (8,11)
             (8,12) (2,13) (12,14)

  selection: (1,4) -> (5,7) -> (8,11) -> (12,14)  = 4 activities

Tests double-loop bubble sort on tuple array with let-pattern
destructure for swap-key extraction, in-place swap of tuple cells.

192 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -1,5 +1,6 @@
 {
   "abundant.ml": 21,
+  "activity_select.ml": 4,
   "ackermann.ml": 125,
   "adler32.ml": 300286872,
   "anagram_check.ml": 2,