Overview of the Issue

During topo server outages, watchers continue to call subscribers every second with the same cached data.
This causing unnecessary plan cache clearing in vtgate for VSchema watcher.
It results in latency hits when the system should be operating normally from cached data.

Reproduction Steps

Reproduction

1. Start vtgate with normal VSchema
2. Simulate 10-minute topo outage (500 errors)
3. Observe multiple VSchemaUpdate calls during outage
4. Each call clears plan cache unnecessarily

Binary Version

main

Operating System and Environment details

NA

Log Fragments