Add codespell support (config, workflow to detect/not fix) and make it fix some typos

[yarikoptic]

More about codespell: https://github.com/codespell-project/codespell .

I personally introduced it to dozens if not hundreds of projects already and so far only positive feedback.

CI workflow has 'permissions' set only to 'read' so also should be safe.

It was requested a while back in

• https://github.com/BerriAI/litellm/pull/10232#issuecomment-2826300701

and recommended in

• https://github.com/BerriAI/litellm/issues/5991#issuecomment-2388853171

there indeed could be some false positives but I think it is quite robust -- you can see how few I had to exclude, and some of those could actually be "fixed" to make it cleaner

[vapier]

can you attach a full run with these settings against the existing docs ? or are they all clean other than the fixes you included ?