feat(notebooks/algorithms/hubs)📊: enhance interactivity, add ECDF vs histogram comparison, and improve exercise structure in hubs notebook

- Add matplotlib as a dependency and update marimo version for improved plotting support.
- Hide code for introductory and instructional cells to improve notebook readability.
- Refactor markdown cells to use dedented triple-quoted strings for better formatting.
- Add new interactive exercise cells for ECDF and histogram comparison, including a slider for bin count.
- Clarify and expand exercise prompts and solution scaffolding for degree centrality and node order analysis.
- Ensure all plotting cells call plt.show() for consistent output in interactive environments.
- Improve guidance and structure for user-implemented answers in exercise cells.

Author: ericmjl