Lower log precision if possible

If you were an attacker bent on traffic analysis, wouldn't you love it if logs were kept with microsecond precision?

Unfortunately, this is what journald does by default. Our tracing_appender file logs and our console logs do the same.

It would probably be better to reduce this precision. In C tor, it's configurable, with a 1-second default.

This should be fairly easy to fix with the console and file logs; with journald, who knows.