chore: import upstream snapshot with attribution

test/sample-targets/variable-duration/variable_duration.ml

@@ -0,0 +1,23 @@
+(** Program for testing magic-trace with operations that take a variable amount of time
+    measured using [mark_start]. *)
+
+open! Core
+
+let[@inline never] do_delay () = ignore (Core_unix.nanosleep 0.000_1 : float)
+let min_dur = Magic_trace.Min_duration.of_ns 700_000
+
+let[@inline never] variable_delay n =
+  Magic_trace.mark_start ();
+  let trailing_ones = Ocaml_intrinsics.Int.count_trailing_zeros (lnot n) in
+  let delays = trailing_ones + 1 in
+  for _ = 1 to delays do
+    do_delay ()
+  done;
+  if Magic_trace.Min_duration.over min_dur then Magic_trace.take_snapshot_with_arg delays
+;;
+
+let () =
+  for i = 1 to 10_000 do
+    variable_delay i
+  done
+;;