test: give hypothesis a little more time

Had a test fail with:

```
hypothesis.errors.DeadlineExceeded: Test took 254.25ms, which exceeds the deadline of 200.00ms
```

Author: nedbat

tests/test_numbits.py

@@ -28,7 +28,7 @@
 # When coverage-testing ourselves, hypothesis complains about a test being
 # flaky because the first run exceeds the deadline (and fails), and the second
 # run succeeds.  Disable the deadline if we are coverage-testing.
-default_settings = settings()
+default_settings = settings(deadline=400)   # milliseconds
 if env.METACOV:
     default_settings = settings(default_settings, deadline=None)