Bugfix: serialize runs in a background thread

[gusostow]

This is endpoint is only called by the apsis runs CLI command. It blocks the event loop for 60s in our environment if called without filters.

Note that I'm going to have to do something about a potential full run store query in the same method, once that is slower from serving the run store from sqlite instead of memory #538.

apsis/python/apsis/service/api.py

Lines 484 to 490 in 64be4c4

	when, runs = apsis.run_store.query(
	run_ids=run_id,
	job_id=job_id,
	state=None if state is None else to_state(state),
	since=since,
	with_args=args,
	)

[LudovicoRighi]

I've reviewed this PR now, please see:

• Add regression test for the GET /api/v1/runs endpoint #540