Add turnstiles, more sched fixes

sched/internal.h

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: ISC
+
+#pragma once
+
+#include <zinnia/sched.h>
+
+errno_t task_create_current(const char* name, struct vma* space, struct task** out);
+
+bool sched_update_priority_locked(struct task* task);