FIX TypeError: normal_() got an unexpected keyword argument 'generator' #723

[earlytobed]

This PR fixes #723, older PyTorch versions (pre-2.2, roughly, 7fc2929) don’t support arg generator, leading to the error:

Traceback (most recent call last):
    ...
    File "~/llm.c/train_gpt2.py", line 160, in _init_weights
    torch.nn.init.normal_(module.weight, mean=0.0, std=0.02, generator=self.init_rng)
TypeError: normal_() got an unexpected keyword argument 'generator'

after commit 86682af : torch.nn.init.normal_ called with generator, file: train_gpt2.py line146, line150

This PR replaces the torch.nn.init.normal_ with Tensor.normal_, ensuring compatibility with older PyTorch releases.