"maximum recursion depth" error when copy.deepcopy(unet) in gen_img.py

### Reproduce
Using v1-5-pruned.safetensors in https://huggingface.co/runwayml/stable-diffusion-v1-5/tree/main

Add
```
import copy
copy.deepcopy(unet)
```
after this line
https://github.com/kohya-ss/sd-scripts/blob/f9317052edb4ab3b3c531ac3b28825ee78b4a966/gen_img.py#L1556

### Error stack trace

```
File "/home/tsogzark/miniconda3/envs/kohyass/lib/python3.10/copy.py", line 172, in deepcopy
y = _reconstruct(x, memo, *rv)
File "/home/tsogzark/miniconda3/envs/kohyass/lib/python3.10/copy.py", line 272, in _reconstruct
if hasattr(y, '__setstate__'):
File "/home/fz/mydisk/Zqh/Cv/kohya_ss/sd-scripts/library/original_unet.py", line 1709, in __getattr__
return getattr(self.delegate, name)
File "/home/fz/mydisk/Zqh/Cv/kohya_ss/sd-scripts/library/original_unet.py", line 1709, in __getattr__
return getattr(self.delegate, name)
File "/home/fz/mydisk/Zqh/Cv/kohya_ss/sd-scripts/library/original_unet.py", line 1709, in __getattr__
return getattr(self.delegate, name)
[Previous line repeated 991 more times]
RecursionError: maximum recursion depth exceeded
```

### Extra infomation
- It works when deepcopy unet in sdxl_gen_img.py
- It works well when remove these two lines.

Reproduce the failure in gen_img.py around line 1556 using v1-5-pruned.safetensors. Then inspect library/original_unet.py around line 1709 and compare the deepcopy path with sdxl_gen_img.py, where it reportedly works. Done means copy.deepcopy(unet) completes without the recursion error.

Written by the indexing model from the issue text.