An engine agonistic parser

[xiki-tempula]

I'm thinking of an engine agonistic IO that would load a dataframe directly from a file and save it to a file and read it back.
I think the pyarrow implementation of the parquet is a good choice where it faithfully reproduce the complex index that we are using.

The interface that i'm thinking of would be

from alchemlyb.parsing.parquet import extract_dHdl, extract_u_nk
import pandas as pd

u_nk.to_parquet(path='u_nk.parquet', index=True)
dHdl.to_parquet(path='dHdl.parquet', index=True)

new_u_nk = extract_u_nk('u_nk.parquet', T=300)
new_dHdl = extract_dHdl('dHdl.parquet', T=300)

assert new_u_nk==u_nk
assert new_dHdl==dHdl