Add mjData.nA the number of non-zeros in the constraint inverse inertia matrix.

PiperOrigin-RevId: 714076988
Change-Id: I4c323a6e81dfb23f7972b662719bbcb688bacf4a

introspect/structs.py

@@ -4701,6 +4701,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  type=ValueType(name='int'),
                  doc='number of non-zeros in constraint Jacobian',
              ),
+             StructFieldDecl(
+                 name='nA',
+                 type=ValueType(name='int'),
+                 doc='number of non-zeros in constraint inverse inertia matrix',
+             ),
              StructFieldDecl(
                  name='nisland',
                  type=ValueType(name='int'),
@@ -5797,7 +5802,7 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                      inner_type=ValueType(name='int'),
                  ),
                  doc='column indices in sparse AR',
-                 array_extent=('nefc', 'nefc'),
+                 array_extent=('nA',),
              ),
              StructFieldDecl(
                  name='efc_AR',
@@ -5805,7 +5810,7 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                      inner_type=ValueType(name='mjtNum'),
                  ),
                  doc="J*inv(M)*J' + R",
-                 array_extent=('nefc', 'nefc'),
+                 array_extent=('nA',),
              ),
              StructFieldDecl(
                  name='efc_vel',