copying: fold in graph copying (shared nodes, cycles, identity-map fix), serialization rules (constructors, record canonical constructor, ObjectInputFilter), record array components, clone() as a defensive copy, two more compile-error exhibits; 24 tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b4BL3cEPHQTk2McE7C

copying/src/broken/ForgotToOverride.java

@@ -0,0 +1,13 @@
+/** Implements Cloneable but forgets to override clone(), then calls it. Does not compile. */
+public class ForgotToOverride {
+
+    static class Foo implements Cloneable {
+        int x = 1;
+    }
+
+    public static void main(String[] args) {
+        Foo foo = new Foo();
+        Object copy = foo.clone();
+        System.out.println(copy);
+    }
+}