Port multi-task unit tests from pipecat-subagents

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.

.github/workflows/coverage.yaml

@@ -41,7 +41,9 @@ jobs:
             --extra google \
             --extra langchain \
             --extra livekit \
+            --extra pgmq \
             --extra piper \
+            --extra redis \
             --extra runner \
             --extra sagemaker \
             --extra tracing \

.github/workflows/tests.yaml

@@ -45,7 +45,9 @@ jobs:
             --extra google \
             --extra langchain \
             --extra livekit \
+            --extra pgmq \
             --extra piper \
+            --extra redis \
             --extra runner \
             --extra sagemaker \
             --extra tracing \