time: add sleep

clock_nanosleep with EINTR restart from the kernel remainder.

lib/time/timetest.ww

@@ -157,3 +157,12 @@ import time;
 	assert(!(time.compare(a, b) != -1i8));
 	assert(!(time.compare(b, a) !=  1i8));
 };
+
+@test fn sleepmonotonic() void = {
+	let before: time.instant = time.now(time.clock.monotonic);
+	time.sleep((5i64 * (time.millisecond: i64)): time.duration,
+	    time.clock.monotonic);
+	let after: time.instant = time.now(time.clock.monotonic);
+	let elapsed: i64 = time.diff(before, after): i64;
+	assert(!(elapsed < 5i64 * (time.millisecond: i64)));
+};