max_shard_size

### Describe the bug

max_shard_size=1GB is set but the size of each safetensor is still greater than 1GB

### Reproduction

pipe.save_pretrained(save_directory='FLUX.1-dev-Control-all', max_shard_size="1GB")

### Logs

```shell

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### System Info

diffusers=0.30.2
accelerate=1.7.0
transformers=4.52.4

### Who can help?

_No response_