adding clock system call

library/runtime/system.zig

@@ -27,6 +27,16 @@ pub fn sleep(ms: usize) void {
     _ = sc.systemCall1(.sleep, ms);
 }
 
+/// Monotonic nanoseconds since boot — a time source for timeouts and short delays. It
+/// only ever moves forward. This is *not* wall-clock time (no date, no timezone — that
+/// is a user-space service layered on top). Deadline pattern for a bounded poll loop:
+///
+///     const deadline = clock() + timeout_ns;
+///     while (clock() < deadline) { ... }
+pub fn clock() u64 {
+    return @intCast(sc.systemCall0(.clock));
+}
+
 /// End the process. Never returns.
 pub fn exit(code: usize) noreturn {
     _ = sc.systemCall1(.exit, code);