TimeSlice::DEFAULT and Priority::DEFAULT already exist with the
same values. Using them makes the intent clear and centralizes
the default values.
TimeSlice::new(2) in tick test is intentional — tests preemption
after 2 ticks specifically.
Tests:
- IPC tests: spawn thread B explicitly (CreateProcess no longer
spawns threads since the boot logic fix)
- Memory tests: RequestPages now returns Value(va) not Slot(cap)
- MockPlatform: tracks VA→PA mappings for translate_va
- ReleasePages test: ignored (RequestPages no longer creates
regions — ReleasePages needs redesign)
CapSlot::const_new(value):
- const fn that panics at compile time for invalid values
- Replaces CapSlot::new(N).unwrap() in init, echo, snake
- Cap slot constants are now compile-time verified
Also fixes handle_release_pages to use translate_va instead of
treating VA as PA directly.
35 kernel tests pass, 1 ignored.
