Move ZMQ socket bind to poll thread to prevent blocking

[ypcisco]

Why I did it

• In scale scenarios, zmq_bind() can take significant time to complete
• Orchestration agent gets blocked during ZmqServer initialization
• Synchronous bind in main thread delays startup and impacts system responsiveness

How I did it

• Moved zmq_bind() call from ZmqServer::bind() to mqPollThread()
• Socket creation and configuration remain in main thread
• Actual bind operation now happens in background poll thread

[anish-n]

Could we add some more details about what scale scenario causes zmq bind to be slow, and how does that scenario result in slowness?

[ypcisco]

Could we add some more details about what scale scenario causes zmq bind to be slow, and how does that scenario result in slowness?

@anish-n this PR doesn't resolve the zmq_bind slowness but prevents it from blocking orchagent. We don't yet know what causes zmq_bind to take 4-5 minutes during scale scenarios.