asynced: allow fps() to ignore the first run and to catch up.

hw/asynced.py

@@ -7,13 +7,17 @@ def delay(secs: float) -> generator:
         yield None
 
 
-def fps(dt: float):
+def fps(dt: float) -> generator:
+    yield None
     until = time.monotonic() + dt
     while True:
         remain = until - time.monotonic()
-        until += dt
         if remain > 0:
             time.sleep(remain)
+        until += dt
+        if remain < -dt:
+            # Catch up a bit
+            until += -remain / 3
         yield None