The PGMQ and Redis bus modules raise an ``Exception`` at import time
when the optional ``pgmq`` / ``redis`` packages are missing, which broke
``pytest`` collection in environments without those extras (e.g. CI
that uses ``--no-extra gstreamer --no-extra local``). Wrap the imports
in ``try/except`` and ``raise unittest.SkipTest`` so the whole test
module is skipped cleanly instead of failing collection.
Brings over 215 tests across 15 files covering the new
multi-task framework: BaseTask / PipelineTask bus lifecycle,
job RPC and job groups, the bus message hierarchy and serializers,
TaskBus + AsyncQueueBus + RedisBus + PgmqBus (with direct and
isolated backends), TaskRegistry, the BusBridgeProcessor, the
WebSocket proxy tasks, the LLMTask deferral logic, and the
PipelineRunner spawn-and-attach flow.
