feat: implement core initialization and local APIC setup

kernel/include/memory/pagetable.h

@@ -25,12 +25,12 @@ struct PageTable {
     };
 
     static PageTable fromCurrent();
+    static optional<PageTable> allocNew();
 
     void activate();
     bool map(void* vaddress, paddr_t paddress, flags_t flags);
     void unmap(void* vaddress);
     optional<info_t> get(void* vaddress);
 
-private:
     paddr_t l4;
 };