This mitigates a side effect of the global current_time and monotonic_time being updated on every server call's timeout, where the end time of any unrelated server call is moved into the future (depending on the frequency of server calls).
By using a more granular timeout, the overall frequency of server calls doesn't have as great of an effect on each individual timeout, as we don't have to wait for an entire millisecond (which was due to the ceiling operation in get_next_timeout).
This [issue](https://bugs.winehq.org/show_bug.cgi?id=57849) gives a few examples of this causing significant degradation in the behavior of some games, which use alertable (server) waits for their FPS limiter.
-- v8: server: Use epoll_pwait2 for the main loop on Linux. server: Use a high precision timespec directly for poll timeouts on supported platforms.