🔗 Implement Fundamental Weak Reference Architecture - Phase 2: Auto-Nil Mechanism

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

test_working_weak_demo.nyash

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+// Working demonstration of weak reference auto-nil behavior
+
+box Parent {
+    init { name }
+    
+    pack(parentName) {
+        me.name = parentName
+    }
+    
+    getName() {
+        return me.name
+    }
+}
+
+box Child {
+    init { weak parent }  // weak modifier on parent field
+    
+    setParent(p) {
+        me.parent = p
+    }
+    
+    getParentInfo() {
+        // This method will use the weak field access system
+        // which automatically returns null if the parent is dropped
+        if me.parent == 0 {
+            return "Parent is null (dropped)"
+        } else {
+            return "Parent exists"
+        }
+    }
+    
+    // Direct weak field access for testing
+    accessWeakParent() {
+        return me.parent
+    }
+}
+
+static box Main {
+    main() {
+        print("=== Weak Reference Auto-Nil Demonstration ===")
+        
+        local parent = new Parent("TestParent")
+        local child = new Child()
+        
+        print("Step 1: Setting up parent-child relationship")
+        child.setParent(parent)
+        print("After setup: " + child.getParentInfo())
+        
+        print("Step 2: Simulating parent 'drop' (set to 0)")
+        parent = 0  // This should trigger weak reference invalidation
+        
+        print("Step 3: Checking child's parent reference after drop")
+        print("After drop: " + child.getParentInfo())
+        
+        print("Step 4: Direct weak field access test")
+        local directAccess = child.accessWeakParent()
+        
+        return "Auto-nil demonstration completed successfully"
+    }
+}