AutoNAT v2 dialerHost should not have the UDP black hole detector

Nobody has claimed this yet.

This issue distills findings from a systematic cross-implementation evaluation of AutoNAT v2, conducted by [ProbeLab](https://probelab.io/). The final report of the investigation is available in the following [link](https://github.com/probe-lab/autonat-perf-audit/blob/main/docs/final-report.md).

The AutoNAT v2 `dialerHost` shares the main host's UDP black hole counter in read-only mode [config.go#L240-L246](https://github.com/libp2p/go-libp2p/blob/v0.48.0/config/config.go#L240-L246). Read-only mode treats any state other than `Allowed` as `Blocked` [black_hole_detector.go#L254-L262](https://github.com/libp2p/go-libp2p/blob/v0.48.0/p2p/net/swarm/black_hole_detector.go#L254-L262), so when the main host is in `Probing` (zero history), the dialerHost refuses every QUIC dial-back with `E_DIAL_REFUSED`.

Observed behaviour:

- Fresh servers, low-traffic nodes, and isolated testbeds can stay in `Probing` → every QUIC dial-back is refused.
- `E_DIAL_REFUSED` is discarded from v2 confidence by [AddRefusal](https://github.com/libp2p/go-libp2p/blob/v0.48.0/p2p/host/basic/addrs_reachability_tracker.go#L689-L692) (it does not call `AddOutcome`), so the client's QUIC address doesn't flip to Unreachable — but it never accumulates positive evidence either, and stays stuck in `Unknown`.
- AutoNAT v1 had the same problem and was fixed in [[#2529](https://github.com/libp2p/go-libp2p/pull/2529)](https://github.com/libp2p/go-libp2p/pull/2529) by disabling the detector on the v1 dialer entirely.

Proposal: apply the v1 approach — pass `nil` counters to `makeAutoNATV2Host()` so the detector doesn't run on the dialerHost. The dialerHost only dials addresses clients explicitly request to test; the detector has no useful role there.

Start at makeAutoNATV2Host and inspect the counter wiring referenced in config/config.go, then review the read-only behavior in p2p/net/swarm/black_hole_detector.go. Compare the AutoNAT v1 fix in #2529 and verify that the v2 dialerHost no longer refuses requested QUIC dial-backs because of the main host's detector state.

Written by the indexing model from the issue text.