Every connection emits a spurious first heartbeat

redis-py's PubSub.subscribe() deliberately leaves its own subscription-confirmation message sitting in the connection's read queue rather than consuming it. That confirmation is still sitting there the first time event_stream()'s main loop reads a message, and the loop currently can't distinguish it from genuinely nothing having happened, so it emits a heartbeat immediately instead of waiting out a real interval. This inflates the heartbeat counter by exactly one for every single connection regardless of how idle it actually was, quietly corrupting any alerting built on heartbeat rate, and it makes any monitor or test that expects the first thing it reads to be real content see a bogus heartbeat instead -- a source of flaky, hard-to-explain failures in exactly the tooling meant to catch real problems.

event_stream() no longer drains the subscription-confirmation message redis-py's subscribe() leaves behind, so the very first get_message() call in the main loop reads that leftover confirmation instead of waiting on real traffic.

See practice_tickets/tests/test_ticket_08_spurious_heartbeat_on_connect.py: connect with nothing else published at all, and measure how long the first heartbeat takes to arrive -- it shows up almost instantly instead of after a genuine heartbeat_interval-length wait.

This is a real gotcha in redis-py's pub/sub API, not an obvious mistake -- subscribe() not consuming its own confirmation is documented but easy to miss, and the fix only makes sense once you know the confirmation is sitting there at all. It's completely invisible in a quick read of event_stream(), since every line individually looks correct.

Right after await pubsub.subscribe(channel) succeeds, and before anything relies on get_message() meaning "nothing happened," there needs to be exactly one throwaway read that consumes whatever subscribe() left behind. Using this connection's heartbeat_interval as that one call's timeout keeps it correct even if the confirmation takes a moment to arrive.