* Clean up the networking_flow directory
- Add networking_flow/README.md covering max-flow / min-cut, with a
file-by-file table and guidance on which algorithm to use.
- minimum_cut.py: add a module docstring with a Wikipedia URL, type
hints, and corner-case doctests; work on a copy so the input graph is
no longer mutated.
- Add dinic.py: Dinic's algorithm (BFS level graph + DFS blocking flow),
adjacency-list based so it handles parallel edges and sparse graphs.
- Add push_relabel.py: the Goldberg-Tarjan push-relabel (preflow) method
with highest-label selection.
Both new algorithms are fully type-hinted, documented with a Wikipedia
reference, and validated by doctests; their output was cross-checked
against ford_fulkerson.py on thousands of random graphs.
* Address review: drop __future__ import, use descriptive names, apply README wording
