Fix flaky test: test pubsub numsub #4924

[hank95179]

Description

This PR fixes the flaky test test pubsub numsub tracked in #4924.

Similar to other PubSub tests in Cluster mode, PUBSUB NUMSUB relies on metadata propagation across nodes. The test was failing intermittently because it checked the subscription count on a different client immediately after subscription. Due to network latency or Gossip delays, the node often reported 0 subscribers instead of the expected count.

Changes

• Replaced the immediate assertion with a polling loop.
• The test now continuously checks pubsubNumSub results until the returned subscriber counts match the expected values (or times out), allowing time for propagation.

Verification

• Reproduction: I used a script to flood the cluster bus with noise, forcing propagation delays which consistently reproduced the Expected: x, Received: 0 failure.
• Fix Verification: Verified that the test stabilizes and passes with the retry logic under the same stressed environment.

Related Issue

Fixes #4924