swarm.DialError should wrap DialError.DialErrors

[sukunrt]

Almost all of the users of swarm.DialError either expect swarm.DialError to wrap over errors of individual dials. To summarise this should return true

errors.Is(
		&DialError{
			Peer:       "pid",
			DialErrors: []TransportError{
			{ 
              Address: ma.StringCast("/ip4/1.2.3.4/tcp/1234"), 
			  Cause: ErrDialBackoff}
			},
		},
		ErrDialBackoff,
	)

I think this is a reasonable thing to fix. Some previous discussion here: #2414 (comment)

There are a lot of usecases here:
https://github.com/search?q=swarm.DialError&type=code

A few examples:

https://github.com/ipni/cassette/blob/ca08e5af7376dc249cbb3a1173bbc6b37e38ceea/metrics.go#L301-L309

		case *swarm.DialError:
			errKind = "dial-error"
			for _, de := range e.DialErrors {
				if de.Cause.Error() == "dial backoff" {
					errKind = "dial-backoff"
					break
				}
			}

https://github.com/libp2p/go-libp2p-kad-dht/blob/ee95d1ab03c47aab03218e18d07483f51e7787e4/fullrt/dht.go#L315

dialErr, ok := err.(*swarm.DialError)
				if ok {
					for _, transportErr := range dialErr.DialErrors {
						if errors.Is(transportErr.Cause, network.ErrResourceLimitExceeded) {
							limitErrOnce.Do(func() { logger.Errorf(rtRefreshLimitsMsg) })
						}
					}
				}

https://github.com/smartcontractkit/libocr/blob/82b910bef5c1c95cc7a886091ccfc1895bde76f5/networking/ocr_endpoint_v1.go#L428

		if !errors.Is(err, swarm.ErrDialBackoff) {