add FlashDateSeparators for time separator config

[mmenanno]

This adds the option to flash the time separators. Found the details around it here https://macos-defaults.com/menubar/flashdateseparators.html#set-to-false-default-value and was able to get it working in my config under:

CustomUserPreferences = {
  "com.apple.menuextra.clock" = {
    FlashDateSeparators = true;
  };
};

With this change you should now be able to do:

menuExtraClock = {
  FlashDateSeparators = true;
};

[mmenanno]

@Craz1k0ek any idea why two of the tests are failing for me? The error message is unclear to me.

[Craz1k0ek]

@mmenanno clueless. Might have to do with the default value. You've set it to false, but null might be better

[mmenanno]

Looks like that fixed it ✅ There is a non-required test that failed, but I believe that is just a flaky test as it is complaining about something unrelated.