GRPC file handles not closing

[ross-spencer]

We've been running COOP as a long-running service for a decent while now. Every so often, we're seeing services stop with too many open file handles: Network.Socket.accept: resource exhausted (Too many open files):

• https://github.com/orcfax/Incidents/issues/10 (coop-publisher)
• https://github.com/orcfax/Incidents/issues/13 (json-fs-store)

Are there any known improvements in the underlying GRPC libraries that we can leverage here to prevent this? Or is there something else we can see in the code that might have been missed preventing file handles from being closed?