Add law of total probability notebook

[Haleshot]

📝 Summary

Followed the Law of Total Probability chapter chapter, got an initial draft up and running.

Appropriate markdown + LaTeX used to explain the concept.
Added:

• Example to explain the concept and functions implemented.
• Interactive example relevant to the topic at hand.
• A tree diagram to explain partitional (non-overlap).

Checkout the notebook here: http://marimo.app/https://github.com/marimo-team/learn/blob/751d19f2a2c56e34509926d858d7a263e462fb46/probability/07_law_of_total_probability.py

📋 Checklist

• I have included package dependencies in the notebook file using --sandbox
• If adding a course, include a README.md
• Keep language direct and simple.

[Haleshot]

Let me know if this is too much for this concept and I can remove the interactive example if you feel it's not very relevant.