Add MLP Mixer on architectures

[HenryMantilla]

Description

Added MLP Mixer architecture proposed in "MLP-Mixer: An all-MLP Architecture for Vision"

Checklist

Ensure your pull request meets the following requirements:

• I have reviewed existing notebooks to avoid duplications.
• My notebook is fully executed.
• I have included a list of all libraries and their versions used in the notebook.
• The notebook file is named clearly to reflect the topic (e.g., cross-entropy-loss.ipynb).
• I have placed the notebook in the appropriate directory under notebooks/.
• My code is simple, precise, and adheres to good coding practices.

[guillepinto]

That's great, thank you. Just a comment, you are not using the image size parameter, you could remove it, although I can approve it that way.

[HenryMantilla]

Solved unused parameter in patch embedding class