ocaml: phase 5.1 lru_cache.ml baseline (cap=3 LRU, fingerprint 499)

Functional LRU cache via association-list ordered most-recent-first.
Get / put both:
  - find or remove the existing entry
  - cons the fresh (k, v) to the front
  - on put, trim the tail when over capacity

Sequence:
  put 1 100; put 2 200; put 3 300
  a = get 1  -> 100  (moves 1 to front)
  put 4 400          (evicts 2)
  b = get 2  -> -1   (no longer cached)
  c = get 3  -> 300
  d = get 1  -> 100
  a + b + c + d = 499

Tests `match … with (k', v) :: rest when k' = k -> …` tuple-cons
patterns with `when` guards, `function` keyword for arg-less
match, recursive find/remove/take over the same list.

Parser limit found: `match n, lst with` ad-hoc tuple-scrutinee is
not yet supported (got "expected op -> got op ,"); workaround
uses outer `if` plus inner match.

171 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -82,6 +82,7 @@
   "floyd_warshall.ml": 9,
   "lis.ml": 6,
   "list_ops.ml": 30,
+  "lru_cache.ml": 499,
   "luhn.ml": 2,
   "magic_square.ml": 65,
   "mat_mul.ml": 621,