Gene Normalizer DB Connection is Constantly Closed

[bencap]

See https://us-west-2.console.aws.amazon.com/cloudwatch/home?region=us-west-2#logsV2:log-groups/log-group/$252Faws$252Felasticbeanstalk$252Fmavedb2-prod-worker-env$252Fvar$252Flog$252Feb-docker$252Fcontainers$252Feb-current-app$252Fstdouterr.log/log-events/i-0d57424da8febff72

When we run worker jobs on stale connections they are constantly closed and cause mapping to fail. It seems this is related to the following lines:

dcd_mapping2/src/dcd_mapping/lookup.py

Lines 160 to 172 in 374672a

	class GeneNormalizerBuilder:
	"""Singleton constructor for Gene Normalizer instance."""
	def __new__(cls) -> QueryHandler:
	"""Provide Gene Normalizer instance. Construct it if unavailable.
	:return: singleton instance of ``QueryHandler`` for Gene Normalizer
	"""
	if not hasattr(cls, "instance"):
	db = create_db()
	q = QueryHandler(db)
	cls.instance = q
	return cls.instance

We should probably just create new instances of the db that do not have their connections closed instead of checking the instance state.