feat(domain): add memory module with page pool, per-process tracking, and region table

crates/domain/src/memory/process_memory.rs

@@ -0,0 +1,47 @@
+use types::id::ProcessId;
+
+use crate::error::KernelError;
+
+pub struct ProcessMemory {
+    process: ProcessId,
+    page_count: usize,
+    limit: usize,
+}
+
+impl ProcessMemory {
+    pub fn new(process: ProcessId, limit: usize) -> Self {
+        Self {
+            process,
+            page_count: 0,
+            limit,
+        }
+    }
+
+    pub fn process(&self) -> ProcessId {
+        self.process
+    }
+
+    pub fn page_count(&self) -> usize {
+        self.page_count
+    }
+
+    pub fn limit(&self) -> usize {
+        self.limit
+    }
+
+    pub fn grant(&mut self, count: usize) -> Result<(), KernelError> {
+        if self.page_count + count > self.limit {
+            return Err(KernelError::OutOfMemory);
+        }
+        self.page_count += count;
+        Ok(())
+    }
+
+    pub fn release(&mut self, count: usize) -> Result<(), KernelError> {
+        if count > self.page_count {
+            return Err(KernelError::OutOfMemory);
+        }
+        self.page_count -= count;
+        Ok(())
+    }
+}