refactor: move tokenizer_data_utils with the rest of utils, add further unit testing.

[willmj]

Description of the change

Move tokenizer_data_utils.py from /data to /utils with the rest of the utils. Update imports so function calls change from tokenizer_data_utils.tokenizer_and_embedding_resize to tokenizer_and_embedding_resize. Add 3 unit tests:

• Ensure adding special tokens works correctly
• Ensure not adding special tokens doesn't modify tokenizer
• Ensure input and output embeddings are resized properly

How to verify the PR

tox -e py

Was the PR tested

• [x] I have added >=1 unit test(s) for every new method I have added.
• [x] I have ensured all unit tests pass

[github-actions[bot]]

Thanks for making a pull request! 😃 One of the maintainers will review and advise on the next steps.

[aluu317]

Can you resolve the conflicts? I think it might need some code changes