The internal GenServer implementation for the jetstream subscriber, use through the Kite root module.

Connects to the given Jetstream V2 server with the configured collections and dids filters.

Heartbeat ping/pong messages are properly handled. This is important because some servers may clean up inactive connections, and if we're subscribing with filters that mean there's a lot of idle time between events, we would otherwise get the connection closed on us.

Cursors are flushed every @flush_interval rather than per write to avoid unnecessary writes.

Timestamps are used as cursors, over the sequential kind. This was recommended by the Bluesky team because it simplifies failing over between instances during outages.