grpc: don't tear down the shared master connection on a caller's own timeout (#9775)

A Canceled/DeadlineExceeded from the caller's per-request context was
treated like a dead channel: it closed the shared cached ClientConn and
cancelled every other in-flight RPC on it with "the client connection is
closing". Under a burst of concurrent chunk assigns (e.g. a large S3
multipart upload) one slow assign hitting its 10s attempt timeout could
poison the connection for all the rest, cascading into a flood of 500s.

Thread the caller's context into shouldInvalidateConnection and only
invalidate on Canceled/DeadlineExceeded while that context is still live,
which isolates the genuine stale-channel signal (a peer restart behind a
k8s Service VIP). To carry the context, add a ctx parameter to the
existing WithGrpcClient, WithMasterClient, and WithMasterServerClient; the
master assign and volume-lookup paths pass their per-attempt context and
every other caller passes context.Background().

weed/shell/command_cluster_check.go

@@ -114,7 +114,7 @@ func (c *commandClusterCheck) Do(args []string, commandEnv *CommandEnv, writer i
 	for _, master := range masters {
 		for _, volumeServer := range volumeServers {
 			fmt.Fprintf(writer, "checking master %s to volume server %s ... ", string(master), string(volumeServer))
-			err := pb.WithMasterClient(false, master, commandEnv.option.GrpcDialOption, false, func(client master_pb.SeaweedClient) error {
+			err := pb.WithMasterClient(context.Background(), false, master, commandEnv.option.GrpcDialOption, false, func(client master_pb.SeaweedClient) error {
 				pong, err := client.Ping(context.Background(), &master_pb.PingRequest{
 					Target:     string(volumeServer),
 					TargetType: cluster.VolumeServerType,
@@ -137,7 +137,7 @@ func (c *commandClusterCheck) Do(args []string, commandEnv *CommandEnv, writer i
 				continue
 			}
 			fmt.Fprintf(writer, "checking master %s to %s ... ", string(sourceMaster), string(targetMaster))
-			err := pb.WithMasterClient(false, sourceMaster, commandEnv.option.GrpcDialOption, false, func(client master_pb.SeaweedClient) error {
+			err := pb.WithMasterClient(context.Background(), false, sourceMaster, commandEnv.option.GrpcDialOption, false, func(client master_pb.SeaweedClient) error {
 				pong, err := client.Ping(context.Background(), &master_pb.PingRequest{
 					Target:     string(targetMaster),
 					TargetType: cluster.MasterType,