ENH: remove bash execution preambles from cookbook notebooks (#717)

[Abhishek9639]

[ENH] remove bash execution from cookbook notebooks. Closes #717

I’ve removed the bash setup cells from all five cookbook notebooks. These cells were mainly installing packages and cloning the repo, which is only required when running the notebooks on Google Colab.

Since our CI pipeline already installs all required dependencies, before running the notebook tests via nbmake, those setup steps were redundant in this repository.

I double checked that all imports used in the notebooks (numpy, pandas, matplotlib, yfinance, cvxpy, pypfopt) are already covered in pyproject.toml, so no dependency changes were needed.

I also ran the full test suite locally all tests passed.

[Abhishek9639]

@fkiraly,
I’ve opened this PR to address #717. I removed the Colab-specific setup cells (!pip install, git clone, os.chdir) from the five cookbook notebooks since CI already handles dependencies before running the tests. Imports are already covered in pyproject.toml, so no dependency changes were needed. Please review when you get a chance.
If any changes are needed, please let me know.
Thanks