Fix#28386
Current code snippet
```
// get delegator
sd, ok := node.delegators.Get(channel)
if !ok {
err := merr.WrapErrChannelNotFound(channel)
log.Warn("Query failed, failed to get shard delegator for search", zap.Error(err))
return nil, err
}
req, err = node.optimizeSearchParams(ctx, req, sd)
if err != nil {
log.Warn("failed to optimize search params", zap.Error(err))
return nil, err
}
// do search
results, err := sd.Search(searchCtx, req)
```
We could move these into `ShardDelegator`, and directly use sealed
segment num in `Search` methods, also segment num got outside could be
wrong when we specify partitions.
Signed-off-by: chasingegg <chao.gao@zilliz.com>
Gao