feat: add pmm, add vmm, add allocator, create memory management foundation

kernel/src/mem/mod.rs

@@ -0,0 +1,19 @@
+pub mod pmm;
+pub mod address;
+pub mod paging;
+pub mod allocator;
+
+#[allow(dead_code)]
+pub fn init(memmap: &limine::response::MemoryMapResponse, hhdm_offset: u64) {
+    unsafe {
+        pmm::BitmapPMM::init(memmap, hhdm_offset);
+    }
+}
+
+#[allow(dead_code)]
+pub fn get_stats() -> (usize, usize) {
+    unsafe {
+        let pmm = pmm::get_pmm_unchecked(); 
+        (pmm.used_pages(), pmm.total_pages())
+    }
+}