issue with mixin serialization

[not-lain]

Describe the bug

not all init parameters are being captured

Reproduction

I was able to identify where the issue is located and here is a very minimalistic reproducer

from huggingface_hub.utils._typing import is_jsonable
from transformers import AutoConfig

cfg = AutoConfig.from_pretrained("Arabic-Clip/bert-base-arabertv2-ViT-B-16-SigLIP-512-epoch-155-trained-2M")
d = cfg.to_dict() #dict 

is_jsonable(d) # False

Logs

irrelevant

System info

- huggingface_hub version: 0.28.1
- Platform: Linux-6.1.85+-x86_64-with-glibc2.35
- Python version: 3.11.11
- Running in iPython ?: No
- Running in notebook ?: No
- Running in Google Colab ?: No
- Running in Google Colab Enterprise ?: No
- Token path ?: /root/.cache/huggingface/token
- Has saved token ?: False
- Configured git credential helpers: 
- FastAI: 2.7.18
- Tensorflow: 2.18.0
- Torch: 2.5.1+cu124
- Jinja2: 3.1.5
- Graphviz: 0.20.3
- keras: 3.8.0
- Pydot: 3.0.4
- Pillow: 11.1.0
- hf_transfer: N/A
- gradio: N/A
- tensorboard: N/A
- numpy: 1.26.4
- pydantic: 2.10.6
- aiohttp: 3.11.12
- ENDPOINT: https://huggingface.co
- HF_HUB_CACHE: /root/.cache/huggingface/hub
- HF_ASSETS_CACHE: /root/.cache/huggingface/assets
- HF_TOKEN_PATH: /root/.cache/huggingface/token
- HF_STORED_TOKENS_PATH: /root/.cache/huggingface/stored_tokens
- HF_HUB_OFFLINE: False
- HF_HUB_DISABLE_TELEMETRY: False
- HF_HUB_DISABLE_PROGRESS_BARS: None
- HF_HUB_DISABLE_SYMLINKS_WARNING: False
- HF_HUB_DISABLE_EXPERIMENTAL_WARNING: False
- HF_HUB_DISABLE_IMPLICIT_TOKEN: False
- HF_HUB_ENABLE_HF_TRANSFER: False
- HF_HUB_ETAG_TIMEOUT: 10
- HF_HUB_DOWNLOAD_TIMEOUT: 10

[not-lain]

after some more debugging I was able to find out the root of the issue which stems from having integer keys in dictionaries

from huggingface_hub.utils._typing import is_jsonable
a =  {0: 'LABEL_0', 1: 'LABEL_1'} 
is_jsonable(a) # False

[Wauplin]

Thanks for opening the issue. I just opened #2857 to fix this :)