progress: fix progress to not redraw every time there's new data

I think the idea of the code was try do 30 updates per second even if
events arrive at, say, every 20 milliseconds. If we had reset the
timer every time we printed, we would otherwise reset the timer every
40 milliseconds and end up with 25 updates per second. However, a bug
in the code caused it to print every update because it always set the
threshold to print the next update to `now`. I tried to keep what I
think was the intent of the original code while fixing the bug.

cli/src/progress.rs

@@ -61,7 +61,15 @@ impl Progress {
             _ = write!(output, "{}", crossterm::cursor::Hide);
             self.guard = Some(guard);
         }
-        self.next_print = now.min(self.next_print + Duration::from_secs(1) / UPDATE_HZ);
+        let period = Duration::from_secs(1) / UPDATE_HZ;
+        // Try to print periodically by setting the new threshold exactly one period
+        // later
+        self.next_print = self.next_print + period;
+        // But if it's been long enough since last update that we'd effectively print
+        // two updates now, reset the threshold to now.
+        if now >= self.next_print {
+            self.next_print = now + period;
+        }
 
         self.buffer.clear();
         write!(self.buffer, "\r").unwrap();
@@ -260,14 +268,14 @@ mod tests {
         // First output is after the initial delay
         assert_snapshot!(update(INITIAL_DELAY - Duration::from_millis(1), 0.1), @"");
         assert_snapshot!(update(Duration::from_millis(1), 0.10), @"[?25l\r 10% [█▊                ]");
-        // TODO: No updates for the next 30 milliseconds
-        assert_snapshot!(update(Duration::from_millis(10), 0.11), @" 11% [██                ][K");
-        assert_snapshot!(update(Duration::from_millis(10), 0.12), @" 12% [██▏               ][K");
-        assert_snapshot!(update(Duration::from_millis(10), 0.13), @" 13% [██▍               ][K");
+        // No updates for the next 30 milliseconds
+        assert_snapshot!(update(Duration::from_millis(10), 0.11), @"");
+        assert_snapshot!(update(Duration::from_millis(10), 0.12), @"");
+        assert_snapshot!(update(Duration::from_millis(10), 0.13), @"");
         // We get an update now that we go over the threshold
         assert_snapshot!(update(Duration::from_millis(100), 0.30), @" 30% [█████▍            ]");
-        // TODO: Even though we went over by quite a bit, the new threshold is relative
-        // to the previous output, so we don't get an update here
-        assert_snapshot!(update(Duration::from_millis(30), 0.40), @" 40% [███████▎          ][K");
+        // Even though we went over by quite a bit, the new threshold is relative to the
+        // previous output, so we don't get an update here
+        assert_snapshot!(update(Duration::from_millis(30), 0.40), @"");
     }
 }