NOJIRA: Add message bus graph

[CfromBU]

Summary

• Add MessageBusGraph, a composed Graph for publisher -> bus -> subscriber coordination.
• Record bus payload history in graph attributes and fan the merged bus payload out to subscribers.
• Export the component from masfactory and add focused pytest coverage.

Test Plan

• uv run --no-sync --with pytest pytest tests/components/test_message_bus_graph.py -q
• uv run --no-sync python - <<'PY'
from masfactory import MessageBusGraph
print(MessageBusGraph.__name__)
PY
• git diff --check

[AckerlyLau]

Agents interact through two primitives: publish and subscribe. Agents subscribe to the topics they care about, and a router delivers matching messages. New agents with new capabilities can start receiving relevant work without rewiring existing connections.

这里实现的是 publisher-> subscriber graph，不是 message bus pattern