Related to #44620
Related to unstable ut "internal/querycoordv2 TestServer/TestNodeUp"
Introduce SessionWatcher interface to fix race condition and goroutine
leak that caused unstable unit test TestServer/TestNodeUp.
Changes:
- Add SessionWatcher interface with EventChannel() and Stop() methods
- Refactor WatchServices() to return SessionWatcher instead of raw
channel
- Fix cleanup order in QueryCoordV2: stop watcher before session
- Update DataCoord, ConnectionManager to use SessionWatcher
- Add MockSessionWatcher for testing
Fixes race condition between session context cancellation and internal
loop exit. Eliminates goroutine leak by providing explicit lifecycle
management.
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Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>
