issue: #45728
pr: #45730
When mixcoord is in standby mode and shutdown is triggered, the
ProcessActiveStandBy goroutine may panic if context cancellation occurs.
This happens because the error handling didn't check for
context.Canceled errors before panicking.
Changes:
- Add context cancellation check in mix_coord Register() before panic
- Check s.ctx.Err() == context.Canceled and gracefully exit
- Remove unused ForceActiveStandby() function from session_util
This ensures standby mixcoord can shutdown gracefully without panic when
context is cancelled during the standby process.
Signed-off-by: Wei Liu <wei.liu@zilliz.com>
