Fix mixed torch.Tensor and DTensor in generate when use FSDP2 + LoRA (#42436)
* Fix mixed torch.Tensor and DTensor error by registering fsdp forward for trainer.mode.generate
* Apply fsdp forward register when fsdp is enabled
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Co-authored-by: yiminzme <yiminzme@gmail.com>
Co-authored-by: Ferdinand Mom <47445085+3outeille@users.noreply.github.com>