feat(init): add init crate with declarative boot manifest, boot sequence, supervisor and shutdown stubs

Also: make types from_raw/raw const fn, add create_process/kill/delegate/revoke to userspace syscall stubs.

crates/init/src/supervisor.rs

@@ -0,0 +1,7 @@
+use crate::manifest::BootManifest;
+
+pub fn supervise(_manifest: &BootManifest) -> ! {
+    loop {
+        userspace::syscall::yield_now();
+    }
+}