ModelBuilder: Use TRANSFORMERS_CACHE as cache_dir

[jambayk]

Describe your changes

We currently try to infer the transformers cache from environment variables but those are not set most of the time. transformers.utils has a variable which handles this logic internally so we can just use that instead.

Also added some exception handling to remove the intermediate files that the model builder adds to the cache dir. Ideally, the transformers cache and intermediate cache should be dealt separately in order to not pollute the transformers cache.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.
• Is this PR including examples changes? If yes, please remember to update example documentation in a follow-up PR.

(Optional) Issue link