Scale n walks - Githubissues

this fixes #13 to make walk generation scale to hundreds of walks on graph of millions of nodes.

[x] iterate over "epochs" where 1 walk is created for each node in each epoch, and the walks are written to a separate file.
[x] add functionality to write to the file as results arrive
[ ] compare timing with new method
[ ] define location of parquet files better [destination should be a dir; epoch_i could be the name of the files
[ ] tune chunk size for writing to parquet?
[ ] think about if it makes sens to have an object that contains all the inputs used in process_nodes

odissei-lifecourse / layered_walk