Introduce parquet files in `file_reader` and `file_writer`

[nikolaj-funartech]

In io_helpers.py, modify both file_reader and file_writer to introduce parquet files.

Add corresponding tests and be cautious with all consequences of this change.

[nikolaj-funartech]

A first code proposition has been written. Everywhere an .npy can be used, it can be replaced by a .parquet file.