MOSH-99: add job price estimation

[newokaerinasai]

This PR

Adds price estimation to the python client. The client shows a warning whenever the job price is too high.

[blainekasten]

@newokaerinasai fyi - I changed the target branch here to next. That's going to be the default way of developing on this library.

[linear]

MOSH-99 Add a user-facing pricing estimate tool in together-python

Based on the file size and/or other meta information from a file, get a rough token number and estimate pricing for a user.

Expected user experience:

1. A user can get a pricing estimate by calling a python function by providing the right arguments (all required) — model name, training file, validation file, n evals, n epochs
2. A user can get a pricing estimate using CLI, calling the function in chore: go live #1.
3. When a user launches a job in CLI, display a pricing estimate in the confirmation sentence.

See the previous implementation for some example and context: https://github.com/togethercomputer/together-python/pull/23/files