Tokengt for Graph Classification
# What does this PR do?
replaces #21098 
Adds the TokenGT model for graph classification in Transformers.

Done:
- [x] Architecture ported
- [x]  Collator (the model has no tokenizer) and preprocessing

Todo:
- [ ] Test results against original implementation, to make sure they are within precision range.
- [ ] Add checkpoints and make sure they load properly
- [ ] Update doc
- [ ] Update test suite
- [ ] Add model card for the checkpoints once added

## Dependencies
Cython, like Graphormer, and einops. 

Linked to #21079

## Before submitting
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case. (Discussed on Slack)
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

Not tagging anyone for now as this is a draft.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21745). All of your documentation changes will be reflected on that endpoint.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>Oops. Don't mark stale. Hold on ... <|||||>Hi @Raman-Kumar ! Do you need a hand on this PR? :)<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>Hi, @clefourrier, soon I will **must**  complete 
(I was focusing on my new full-time job recently)<|||||>Congrats on your new job! I'll have some time off soon so I'll be less responsive, but feel free to ping me nonetheless!<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>In July Month, I work on this. I have more holiday on that month 