fix: guard connection-state callbacks against no running event loop

The previous hotfix's disconnect()-on-comm-error path can now fire
during server/brewpi.py's own final best-effort hardware-release
cleanup (finally: block's heater.close()/stirrer.activate(False)),
which runs after the event loop has already stopped - previously
nothing about hardware teardown touched an AttributeChange-tracked
field, so this path was dormant. asyncio.create_task() there raises
RuntimeError: no running event loop, crashing the shutdown sequence.

Adds fire_and_forget() (tasks/task.py) - asyncio.create_task() that
silently drops the message instead of raising when there's no loop to
schedule on - and uses it for the Connected/FirmwareVersion broadcasts.
SudTask.check_connections() also now no-ops entirely without a running
loop, since self.sud.stop() cascades into further unguarded
create_task() calls (on_state_changed, heater_task.shutdown(), ...)
that a stopped loop can't help with anyway.

Reproduced and verified fixed directly against HeaterTask/HeaterHendi
with no event loop running (mirrors the exact server/brewpi.py
shutdown-time call path that crashed on the brewpi Pi).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YaPLuRPpyjWcwhMvCvpHCL

tasks/__init__.py

@@ -1,4 +1,4 @@
-from tasks.task import ATask, TaskManager
+from tasks.task import ATask, TaskManager, fire_and_forget
 from tasks.tempsensor import TempSensorTask
 from tasks.heater import HeaterTask
 from tasks.stirrer import StirrerTask