Add some types definitions and node partitionning in.

This is taken from:
https://lab.nexedi.com/xavier_thompson/scan-filesystem/tree/ea6ba5dd5672a65bf5e9e13c3aa7f36fff9c4a08/cython

Raw source code taken from:
https://github.com/scikit-learn/scikit-learn/blob/579e7de7f38f9f514ff2b2be049e67b14e723d17/sklearn/cluster/_kmeans.py#L525

Not functional, just for sake of reference