Implement Phase 6 Box reference operations in MIR/VM - RefNew/RefGet/RefSet/WeakNew/WeakLoad/Barrier*

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

test_field_access.nyash

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+// Test for Phase 6 Box reference operations
+// Simple field access test
+
+static box Main {
+    init { console }
+    
+    main() {
+        me.console = new ConsoleBox()
+        me.console.log("Testing Phase 6 Box reference operations")
+        
+        // Create a simple object
+        local obj
+        obj = new StringBox("Hello")
+        
+        // Test field access
+        local result
+        result = obj.length
+        
+        print("Field access result: " + result)
+        
+        return "Phase 6 test completed"
+    }
+}