Failed to load model after setting user actuator callback

### Description ###
Loading a model with user actuators (using `mujoco.MjModel.from_xml_path`) would fail if a user actuator callback is set (using `mujoco.set_mjcb_act_dyn`, `set_mjcb_act_gain`, or `set_mjcb_act_bias`).

To reproduce the problem:

```python
import mujoco

def my_act_dyn(model, data, id):
return 0.0

mujoco.set_mjcb_act_dyn(my_act_dyn)

model = mujoco.MjModel.from_xml_path("user_act.xml")
```

`user_act.xml`:
```xml

```

Output:
```
Traceback (most recent call last):
File "/home/yushijinhun/robodev/mujoco_act_bug/user_act.py", line 8, in
model = mujoco.MjModel.from_xml_path("user_act.xml")
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: Error: engine error: Python exception raised
```

I tried to debug this problem using GDB and here is the backtrace:
```gdb
#0 mujoco::python::(anonymous namespace)::EscapeWithPythonException () at /tmp/pip-req-build-gqttshg5/mujoco/callbacks.cc:36
#1 0x00007ffff6fa0210 in mujoco::python::(anonymous namespace)::MjWrapperLookup (ptr=0x12d2e00) at /tmp/pip-req-build-gqttshg5/mujoco/callbacks.cc:117
#2 0x00007ffff6fa1195 in mujoco::python::(anonymous namespace)::MjWrapperLookup (ptr=0x12d2e00) at /tmp/pip-req-build-gqttshg5/mujoco/callbacks.cc:122
#3 0x00007ffff6f99ae3 in mujoco::python::(anonymous namespace)::PyMjcbActDyn (m=0x12c95c0, d=0x12d2e00, id=0) at /tmp/pip-req-build-gqttshg5/mujoco/callbacks.cc:208
#4 0x00007ffff6b14e64 in mj_fwdActuation (m=0x12c95c0, d=0x12d2e00) at /home/yushijinhun/repos/mujoco/src/engine/engine_forward.c:257
#5 0x00007ffff6b17569 in mj_forwardSkip (m=0x12c95c0, d=0x12d2e00, skipstage=0, skipsensor=0) at /home/yushijinhun/repos/mujoco/src/engine/engine_forward.c:851
#6 0x00007ffff6b1763f in mj_forward (m=0x12c95c0, d=0x12d2e00) at /home/yushijinhun/repos/mujoco/src/engine/engine_forward.c:865
#7 0x00007ffff6b176cb in mj_step (m=0x12c95c0, d=0x12d2e00) at /home/yushijinhun/repos/mujoco/src/engine/engine_forward.c:877
#8 0x00007ffff6d557f5 in mjCModel::TryCompile (this=0x12c4110, m=@0x7fffffffb128: 0x12c95c0, d=@0x7fffffffb130: 0x12d2e00, vfs_provider=0) at /home/yushijinhun/repos/mujoco/src/user/user_model.cc:2854
#9 0x00007ffff6d51dad in mjCModel::Compile (this=0x12c4110, vfs_provider=0) at /home/yushijinhun/repos/mujoco/src/user/user_model.cc:2442
#10 0x00007ffff6d9cd86 in _loadXML (filename=0x7fffffffd1a0 "user_act.xml", vfs_provider=0, error=0x7fffffffba30 "", error_sz=1024) at /home/yushijinhun/repos/mujoco/src/xml/xml_api.cc:86
#11 0x00007ffff6d9cf2a in mj_loadXML (filename=0x7fffffffd1a0 "user_act.xml", vfs=0x0, error=0x7fffffffba30 "", error_sz=1024) at /home/yushijinhun/repos/mujoco/src/xml/xml_api.cc:116
```

It seems that MuJoCo creates a temporary `mjData` struct and does simulation during model compilation. The simulation calls `mjcb_act_dyn` to calculate activation dynamics. Because the callback function is in Python, the `mjData` has to be wrapped before passing to Python code. However, that temporary `mjData` struct has never been passed to [`MjWrapper`](https://github.com/deepmind/mujoco/blob/93012bf16420d190fdf2e7bbe59e28d128b302f7/python/mujoco/structs.cc#L597)'s constructor to create such wrapper. Therefore, [the lookup of the corresponding wrapper object](https://github.com/deepmind/mujoco/blob/93012bf16420d190fdf2e7bbe59e28d128b302f7/python/mujoco/callbacks.cc#L117) of the `mjData` struct would fail.

### Environment ###
* Operating system: Ubuntu 23.10 (devel) / Linux 6.3.0
* MuJoCo version: 2.3.8 (built from source, commit: https://github.com/deepmind/mujoco/commit/93012bf16420d190fdf2e7bbe59e28d128b302f7)
* Python binding: `mujoco` (Python 3.11.4)