Bound JSON-RPC input by size and nesting depth

Enforce the nesting bound in one parse, capping allocation by depth, not input size.

test/rpc/test_jsonrpc.h

@@ -9,6 +9,8 @@ class TestJsonrpc : public test_fixture {
 
   CPPUNIT_TEST(test_basics);
   CPPUNIT_TEST(test_response_size_limit);
+  CPPUNIT_TEST(test_depth_limit);
+  CPPUNIT_TEST(test_size_limit);
 
   CPPUNIT_TEST_SUITE_END();
 
@@ -18,6 +20,8 @@ public:
 
   void test_basics();
   void test_response_size_limit();
+  void test_depth_limit();
+  void test_size_limit();
 
 private:
   std::unique_ptr<TestMainThread> m_test_main_thread;