Suppress duplicate notifications at update granularity

Change duplicate suppression for a non-atomic notification to fail on individual
updates when multiple are present, instead of failing the whole notification early on a
single bad update.
  1) Prevents accrual of stale leaves due to a single duplicate update failing the whole
     notification (remaining updates not processed).
  2) Allows deletes to independently complete when duplicate updates are present.
  3) Avoids errant implicit deletions, since some updates (including duplicates) will no
     longer be stale due to #1.

Increase test coverage for interaction between updates/deletes/stale leaves and suppression.

PiperOrigin-RevId: 258587893

cache/cache.go

@@ -30,6 +30,7 @@ import (
 	"github.com/golang/protobuf/proto"
 	"github.com/openconfig/gnmi/client"
 	"github.com/openconfig/gnmi/ctree"
+	"github.com/openconfig/gnmi/errlist"
 	"github.com/openconfig/gnmi/metadata"
 	"github.com/openconfig/gnmi/path"
 	"github.com/openconfig/gnmi/value"
@@ -343,12 +344,14 @@ func (t *Target) GnmiUpdate(n *gpb.Notification) error {
 		n.Update = updates
 		n.Delete = deletes
 	}()
+	errs := &errlist.List{}
 	for _, u := range updates {
 		noti := proto.Clone(n).(*gpb.Notification)
 		noti.Update = []*gpb.Update{u}
 		nd, err := t.gnmiUpdate(noti)
 		if err != nil {
-			return err
+			errs.Add(err)
+			continue
 		}
 		t.meta.AddInt(metadata.UpdateCount, 1)
 		if nd != nil {
@@ -365,7 +368,7 @@ func (t *Target) GnmiUpdate(n *gpb.Notification) error {
 		}
 	}
 
-	return nil
+	return errs.Err()
 }
 
 func (t *Target) checkTimestamp(ts time.Time) {