fix: stop leaked watch streams when pool-scope metadata is removed

[WorrierKhushal]

What type of PR is this?

/kind bug

What this PR does / why we need it:

MultiplexerManager.updateLeaderHubConfiguration was supposed to tear
down watch streams for resources removed from pool-scoped-metadata,
but it was querying two dead fields (lazyLoadedGVRCache,
lazyLoadedGVRCacheDestroyFunc) left over from a past refactor — these
were initialized but never populated anywhere, so the cleanup logic
never actually ran. Meanwhile, the real cache instances live in
filterStoreManager, but DeleteFilterStore only removed the map entry
without calling Destroy() on the underlying filterStore, so the
watch stream and its resources (goroutines, memory, network connection)
kept running indefinitely even after the resource was removed from
pool-scoped-metadata.

This PR:

• Makes filterStoreManager.DeleteFilterStore call fs.Destroy()
  before removing the entry.
• Updates updateLeaderHubConfiguration to call
  m.filterStoreManager.DeleteFilterStore(gvrStr) directly instead of
  the dead-map logic.
• Removes the now-unused lazyLoadedGVRCache /
  lazyLoadedGVRCacheDestroyFunc fields.

Added a test verifying that removing a GVR from pool-scoped-metadata
actually invokes Destroy() on its filter store.

Which issue(s) this PR fixes:

Fixes #2753

Special notes for your reviewer:

• go test -v ./pkg/yurthub/multiplexer/... — all tests pass, including the new one
• GOOS=linux go build ./... and go vet ./pkg/yurthub/multiplexer/... — both clean
• grep -r "lazyLoadedGVRCache" pkg/yurthub/ — zero remaining references, confirming safe removal
• No exported function signatures changed

Does this PR introduce a user-facing change?

NONE

other Note

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[WorrierKhushal]

Hi @rambohe-ch @luc99hen @wawlian @carolove Sir i am khushal ,

I have submitted a pull request fixing issue #2753 ([BUG] Multiplexer watch streams leak indefinitely when pool-scope metadata is removed from Leader Hub ConfigMap).

Key Fix Details:

• Implemented explicit fs.Destroy() inside DeleteFilterStore before map cleanup to release goroutines, memory, and active network connections.
• Refactored updateLeaderHubConfiguration to use DeleteFilterStore directly and purged legacy unpopulated fields (lazyLoadedGVRCache).
• Added unit test verification under pkg/yurthub/multiplexer/ to ensure stream teardown when GVR is removed.

All tests (go test -v ./pkg/yurthub/multiplexer/...), go vet, and cross-compilation (GOOS=linux go build ./...) pass cleanly without errors.

Whenever you have some time, could you please take a look and share your feedback? Thanks!