Fix capturing hparams for loggers that don't support serializing non-primitives

[awaelchli]

In the previous version of LitGPT, I added this code to sanitize the hparams for logging:

litgpt/pretrain/tinyllama.py

Line 65 in 8a101b6

hparams = {k: v for k, v in locals().items() if isinstance(v, (int, float, str)) and not k.startswith("_")}

But this code was removed in the new version, causing errors like:

TypeError: Object of type PosixPath is not JSON serializable

(e.g. with wandb)

I plan to improve this in Lightning's .log_hyperparameters() implementation, after which we can remove the function I added here again.

[carmocca]

Does finetuning also need it?

Also please apply the change to the extensions/thunder/pretrain.py copy

[awaelchli]

Finetuning doesn't capture the hparams for the logger. It's only in the training script because it is my personal preference and so far I was the only user of this script that used wandb until today when Guangtao from TinyLlama noticed this bug.