feat(domain): add Thread constructor, accessors, and state machine transitions

crates/domain/src/error.rs

@@ -1,4 +1,8 @@
-use types::{bounded::CapSlot, id::ProcessId, permission::Permission};
+use types::{
+    bounded::CapSlot,
+    id::{ProcessId, ThreadId},
+    permission::Permission,
+};
 
 #[derive(Debug)]
 pub enum KernelError {
@@ -10,4 +14,5 @@ pub enum KernelError {
     WouldBlock,
     TooManyThreadsInProcess,
     TooManyProcesses,
+    InvalidStateTransition(ThreadId),
 }