fix: reduce idle CPU wakeups and deferred-work polling

kernel/src/Timekeeping/ApicTimer.hpp

@@ -11,9 +11,14 @@ namespace Timekeeping {
     // Initialize the APIC timer: calibrate against PIT, start periodic interrupts
     void ApicTimerInitialize();
 
-    // Initialize the APIC timer on an AP (calibrate + start, no IRQ handler registration)
+    // Initialize the scheduler timer on an AP using the BSP calibration.
     void ApicTimerInitializeAP();
 
+    // Idle APs are woken for runnable work by the reschedule IPI, so their
+    // periodic scheduler timer can remain masked until a process is dispatched.
+    void ApicTimerEnterApIdle();
+    void ApicTimerLeaveApIdle();
+
     // Reinitialize the APIC timer after S3 resume using the previously
     // calibrated tick rate. Skips PIT calibration and IRQ registration
     // (both survive in RAM). Only reprograms the timer hardware registers.