A clustering algorithm: walktrap with `PIE` model

Implement a clustering algorithm: walktrap with `PIE` model.

Paper: https://arxiv.org/abs/physics/0512106

Reference implementation: https://cdlib.readthedocs.io/en/latest/reference/cd_algorithms/algs/cdlib.algorithms.walktrap.html#cdlib.algorithms.walktrap

The issue names no GraphScope files, tests, or entry points. Read the linked Walktrap paper and CDlib reference implementation first, then locate the relevant graph-clustering integration in GraphScope. Done means the Walktrap algorithm with the PIE model is implemented.

Written by the indexing model from the issue text.