The plugin loader pre-registers empty shells in sys.modules before
executing any submodule. When _setup.py ran 'from . import _read_mem0_json'
at module level, Python found the empty parent shell (init not yet executed),
so the import failed silently. This left _setup.py partially loaded and
post_setup undefined, causing 'cannot import name post_setup' during
hermes memory setup mem0.
Move the import inside the three functions that use it, matching the
late-import pattern __init__.py already uses for post_setup.
Fixes: hermes memory setup mem0 crashing with ImportError
e8521f47f9