Gemma3 initial commit

[chapman20j]

Resolves #100
Adds the Gemma3 model to the Bonsai Repo. This first commit is just a working version, but I am still working on optimizing it.

Reference
Refer to Issue #100

Checklist

• I have read the Contribution Guidelines and used pre-commit hooks to format this commit.
• I have added all the necessary unit tests for my change. (run_model.py for model usage, test_outputs.py and/or model_validation_colab.ipynb for quality).
• (If using an LLM) I have carefully reviewed and removed all superfluous comments or unneeded, commented-out code. Only necessary and functional code remains.
• I have signed the Contributor License Agreement (CLA).