Make constraint island discovery on by default.

Also fix latent bug in mjData serialization.

PiperOrigin-RevId: 799505349
Change-Id: I299e7cc8133fa2ec0b339a7ff3d02543e06778b1

python/mujoco/introspect/enums.py

@@ -44,7 +44,8 @@ ENUMS: Mapping[str, EnumDecl] = dict([
              ('mjDSBL_EULERDAMP', 16384),
              ('mjDSBL_AUTORESET', 32768),
              ('mjDSBL_NATIVECCD', 65536),
-             ('mjNDISABLE', 17),
+             ('mjDSBL_ISLAND', 131072),
+             ('mjNDISABLE', 18),
          ]),
      )),
     ('mjtEnableBit',
@@ -57,8 +58,7 @@ ENUMS: Mapping[str, EnumDecl] = dict([
              ('mjENBL_FWDINV', 4),
              ('mjENBL_INVDISCRETE', 8),
              ('mjENBL_MULTICCD', 16),
-             ('mjENBL_ISLAND', 32),
-             ('mjNENABLE', 6),
+             ('mjNENABLE', 5),
          ]),
      )),
     ('mjtJoint',

python/mujoco/introspect/enums_test.py

@@ -43,8 +43,7 @@ class EnumsTest(absltest.TestCase):
                                           ('mjENBL_FWDINV', 1<<2),
                                           ('mjENBL_INVDISCRETE', 1<<3),
                                           ('mjENBL_MULTICCD', 1<<4),
-                                          ('mjENBL_ISLAND', 1<<5),
-                                          ('mjNENABLE', 6)))
+                                          ('mjNENABLE', 5)))
 
   # values mostly increment by one with occasional overrides
   def test_mjtGeom(self):  # pylint: disable=invalid-name