chore: add enum benches

Author: timfennis

benches/programs/enumerate_find.ndc

@@ -0,0 +1,6 @@
+// Early-exit search: lazy enumerate avoids allocating tuples
+// for elements past the target.
+let xs = list(0..1_000_000);
+let target = 750_000;
+let found = xs.enumerate().find(fn(p) => p[1] == target);
+print(found);

benches/programs/enumerate_for_loop.ndc

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+// Common pattern: iterate every element with its index.
+// Lazy version avoids allocating an intermediate list of tuples.
+let xs = list(0..500_000);
+let acc = 0;
+for (i, v) in xs.enumerate() {
+    acc += i + v;
+}
+print(acc);

benches/programs/enumerate_take_small.ndc

@@ -0,0 +1,5 @@
+// Lazy enumerate should win big: only the first 10 tuples are needed,
+// but the eager version allocates a full Vec of 1_000_000 tuples first.
+let xs = list(0..1_000_000);
+let head = xs.enumerate().take(10).list();
+print(head.len);

benches/programs/enumerate_to_list.ndc

@@ -0,0 +1,6 @@
+// Worst case for lazy: full materialization to a list.
+// Lazy adds one indirection layer per element; expect a small regression
+// or near-parity here.
+let xs = list(0..500_000);
+let result = xs.enumerate().list();
+print(result.len);