Scheduling and time

To write

Priorities, timeslices and the clock.

Priorities

• base vs. max priority, TaskSetPriority / TaskSetMaxPriority, waiters re-sorted on change

Timeslices

• microseconds, TIMESLICE_MIN/MAX, TaskSetTimeslice

Tickless time

• no periodic tick; one-shot deadlines
• reading the counter from userspace, <zuzu/uptime.h>, counter_freq / counter_boot