Fix Summarize for Colab

Fix for Colab:

set minimum transformer lib (Colab uses one that breaks the Tokenizer constructor on the new model)
truncate summary_groups to ensure they fit in context window

[ ] Commits signed: All commits must be GPG or SSH signed.
[ ] DCO Compliance: Developer Certificate of Origin (DCO) applies to the code, documentation, and any example data provided. Ensure commits are signed off.
[ ] Notebook outputs cleared: Ensure all notebook outputs are cleared.
[ ] Automated testing: Add the recipe to the automated tests.
[x] Test in Google Colab:
- [ ] Test that it works in Google Colab (Python 3.10.12).
- [ ] Colab has its own package set and Python version, so ensure compatibility.
[x] Test locally:
- [ ] Ensure the code works in a fresh Python virtual environment (venv).
[ ] Flexible LLM platform support:
- [ ] The platform should be easily switchable. Use LangChain for now.
- [ ] Include !pip install git+https://github.com/ibm-granite-community/granite-kitchen in the instructions.
[ ] Example data: Follow the example data guidance.
[ ] README.md updates:
- [ ] Add a link to the recipe in the Table of Contents (ToC).
- [ ] Include a Colab button after that link.

ibm-granite-community / granite-snack-cookbook