[chore] update otel libraries (#3740)

* chore: update otel dependencies

* refactor: combine tracing & metrics in observability package

* chore: update example tracing compose file

vendor/google.golang.org/grpc/resolver/resolver.go

@@ -22,6 +22,7 @@ package resolver
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"net"
 	"net/url"
@@ -237,8 +238,8 @@ type ClientConn interface {
 	// UpdateState can be omitted.
 	UpdateState(State) error
 	// ReportError notifies the ClientConn that the Resolver encountered an
-	// error.  The ClientConn will notify the load balancer and begin calling
-	// ResolveNow on the Resolver with exponential backoff.
+	// error. The ClientConn then forwards this error to the load balancing
+	// policy.
 	ReportError(error)
 	// NewAddress is called by resolver to notify ClientConn a new list
 	// of resolved addresses.
@@ -330,3 +331,20 @@ type AuthorityOverrider interface {
 	// typically in line, and must keep it unchanged.
 	OverrideAuthority(Target) string
 }
+
+// ValidateEndpoints validates endpoints from a petiole policy's perspective.
+// Petiole policies should call this before calling into their children. See
+// [gRPC A61](https://github.com/grpc/proposal/blob/master/A61-IPv4-IPv6-dualstack-backends.md)
+// for details.
+func ValidateEndpoints(endpoints []Endpoint) error {
+	if len(endpoints) == 0 {
+		return errors.New("endpoints list is empty")
+	}
+
+	for _, endpoint := range endpoints {
+		for range endpoint.Addresses {
+			return nil
+		}
+	}
+	return errors.New("endpoints list contains no addresses")
+}