feat: rename 'ZenithOS' => 'MontaukOS' and fix build system issues

kernel/src/Memory/PageFrameAllocator.cpp

@@ -124,7 +124,7 @@ namespace Memory {
         }
     }
 
-    void PageFrameAllocator::GetStats(Zenith::MemStats* out) {
+    void PageFrameAllocator::GetStats(Montauk::MemStats* out) {
         if (!out) return;
         Lock.Acquire();
         uint64_t freeBytes = 0;

kernel/src/Memory/PageFrameAllocator.hpp

@@ -29,7 +29,7 @@ public:
         void Free(void* ptr);
         void Free(void* ptr, int n);
 
-        void GetStats(Zenith::MemStats* out);
+        void GetStats(Montauk::MemStats* out);
     };
 
     extern PageFrameAllocator* g_pfa;