Add policies for global attribute conflict resolution upon attach

For example when loading parent_merge.xml:

```
WARNING: Attach conflict when attaching 'child' to 'parent_merge', policy is 'merge'
timestep: parent has 0.005, child has 0.002, taking the minimum
iterations: parent has 50, child has 100, taking the maximum
flag 'Damper': added from child
```

When loading parent_error.xml:

```
XML Error: Attach conflict when attaching 'child' to 'parent_error', policy is 'error'
timestep: parent has 0.005, child has 0.002
iterations: parent has 50, child has 100
Element 'attach', line 10
```
PiperOrigin-RevId: 933620810
Change-Id: Ib477863b5ef763474d27fb4be5a4148be1d5d500

python/mujoco/introspect/structs.py

@@ -6977,6 +6977,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  type=ValueType(name='int'),
                  doc='align free joints with inertial frame',
              ),
+             StructFieldDecl(
+                 name='conflict',
+                 type=ValueType(name='int'),
+                 doc='conflict resolution for attach (mjtConflict)',
+             ),
              StructFieldDecl(
                  name='LRopt',
                  type=ValueType(name='mjLROpt'),