cleanup: replace magic TimeSlice::new(100) and Priority::new(16) with DEFAULT

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.

crates/kernel/src/syscall/lifecycle.rs

@@ -15,7 +15,7 @@ impl<P: Platform> Kernel<P> {
         use domain::thread::SavedContext;
 
         let priority = types::bounded::Priority::DEFAULT;
-        let time_slice = types::time::TimeSlice::new(100);
+        let time_slice = types::time::TimeSlice::DEFAULT;
         let context = SavedContext::with_entry_and_stack(entry, stack);
 
         let tid = match self.threads.spawn_with_context(pid, priority, time_slice, None, context) {
@@ -99,7 +99,7 @@ impl<P: Platform> Kernel<P> {
         };
 
         let priority = types::bounded::Priority::DEFAULT;
-        let time_slice = types::time::TimeSlice::new(100);
+        let time_slice = types::time::TimeSlice::DEFAULT;
         let context = SavedContext::with_entry_and_stack(entry, stack);
 
         let tid = match self.threads.spawn_with_context(target_pid, priority, time_slice, None, context) {

crates/kernel/src/tests/helpers.rs

@@ -23,7 +23,7 @@ pub fn test_kernel() -> Kernel<MockPlatform> {
 pub fn kernel_with_process() -> (Kernel<MockPlatform>, ProcessId) {
     let mut kernel = test_kernel();
     let (pid, _tid) = kernel
-        .boot(Priority::new(16).unwrap(), TimeSlice::new(100))
+        .boot(Priority::DEFAULT, TimeSlice::DEFAULT)
         .unwrap();
     (kernel, pid)
 }

crates/kernel/src/tests/ipc.rs

@@ -29,8 +29,8 @@ fn setup_ipc_kernel() -> (
     let pid_b = ProcessId::from_raw(1);
     let tid_b = k.spawn_thread_for_test(
         pid_b,
-        Priority::new(16).unwrap(),
+        Priority::DEFAULT,
-        TimeSlice::new(100),
+        TimeSlice::DEFAULT,
     );
 
     // Create an endpoint

crates/kernel/src/tests/tick.rs

@@ -18,10 +18,10 @@ fn tick_preempts_when_time_expired_and_other_thread_ready() {
     let mut k = Kernel::new(mock, pool);
 
     // Boot with quantum=2 so it expires after 2 ticks
-    let (pid, tid1) = k.boot(Priority::new(16).unwrap(), TimeSlice::new(2)).unwrap();
+    let (pid, tid1) = k.boot(Priority::DEFAULT, TimeSlice::new(2)).unwrap();
 
     // Spawn a second thread so scheduler has someone to switch to
-    let tid2 = k.spawn_thread_for_test(pid, Priority::new(16).unwrap(), TimeSlice::new(100));
+    let tid2 = k.spawn_thread_for_test(pid, Priority::DEFAULT, TimeSlice::DEFAULT);
 
     // First tick: time remaining
     let d1 = k.handle_tick(CoreId::from_raw(0));