[BUG] ijson is an optional import

[jmmshn]

I think ijson is an optional import for lobster but the lobster import is a part of the mp flow.

atomate2/src/atomate2/lobster/schemas.py

Line 10 in 8b1ee04

import ijson

atomate2/src/atomate2/vasp/flows/mp.py

Line 18 in 8b1ee04

from atomate2.vasp.flows.lobster import VaspLobsterMaker

This leads to import errors when lobster is not installed.

[JaGeo]

Tagging @naik-aakash : maybe enable the Lobster flow only if both LobsterPy and ijson exist in the environment.