优化仿真求解性能并修复流量闭合问题（初版）

tests/test_contact_solver_causalization.py

@@ -162,6 +162,8 @@ class ContactSolverCausalizationTests(unittest.TestCase):
 
         self.assertTrue(diagnostics.success, diagnostics.message)
         self.assertGreater(diagnostics.evaluations, 0)
+        self.assertEqual(diagnostics.jacobian_mode, "dense")
+        self.assertFalse(diagnostics.dense_fallback_used)
         self.assertAlmostEqual(load.pneumatic.p, 41.0, delta=1.0e-3)
         self.assertAlmostEqual(load.mechanical.f, -41.0, delta=1.0e-3)
         self.assertAlmostEqual(contact.contact_force, 41.0, delta=1.0e-3)