Add init command to load base .bin files

[albertpurnama]

@joshcarp this might not be the change that you wanted, but I figured it's the correct direction, but let me know what you think!

Changes

This PR adds a llmgo init command.

What init command does:

1. Check the ~/.cache/llmgo/base directory, if not exist, then create it.
2. Check all files within base directory, if any of the base files (listed below) does not exist, it will try to load it from HF.

Other changes:

• run command now loads the tokenizer before showing stdin. It will return error asking user to run init before run gpt2.

Recording

https://github.com/joshcarp/llm.go/assets/14824254/f3785a6c-c8f7-4156-befc-511984acd6e6

[joshcarp]

I like this and from a general usability perspective i think this is a really good first pass. Gonna merge it just like the other CLI command