fix: PFnano format for dask

[yimuchen]

• Fixing missing parenthesis for nested jet object access
• Adding test file for automatic format tests
• Fix issue where opening the same file multiple files can cause the access to nested structures to fail.

[yimuchen]

This fixes the issue with first time opening, but has a strange side effect if you first open the file with dask and without dask:

from coffea.nanoevents import NanoEventsFactory
from coffea.nanoevents.schemas import PFNanoAODSchema


def open_events(permit_dask=False):
    factory = NanoEventsFactory.from_root(
        "file:./pfnano.root",
        schemaclass=PFNanoAODSchema,
        permit_dask=permit_dask,
    )
    return factory.events()

The following works fine

events = open_events(permit_dask=False)
print(events.Jet.constituents.pf.pt)
events = open_events(permit_dask=False)
print(events.Jet.constituents.pf.pt)

The following is also fine:

events = open_events(permit_dask=False)
print(events.Jet.constituents.pf.pt)
events = open_events(permit_dask=False)
print(events.Jet.constituents.pf.pt)

But the following fails:

events = open_events(permit_dask=True)
print(events.Jet.constituents.pf.pt)
events = open_events(permit_dask=False)
print(events.Jet.constituents.pf.pt)

[lgray]

figured this one out - thanks for isolating this problem, it was really starting to bug me!