Fix duplicate peer usrpwd transport reconciliation

[BOURBONCASK]

Description

What does this PR do?

This PR fixes duplicate peer transport reconciliation when transport.auth.usrpwd is enabled.

The transport layer no longer treats the authenticated principal as part of transport compatibility, and instead stores the usrpwd principal as transport-local metadata. When a duplicate transport is merged, the principal can now be upgraded from Unknown to Known(username) after a successful OpenAck.

The PR also refreshes interceptors after such principal upgrades so that username-based access control sees the updated authenticated principal.

In addition, it adds:

• a transport-level regression test for duplicate peer transport reconciliation with usrpwd
• an integration test covering ACL refresh after a duplicate transport upgrades the principal

Why is this change needed?

In a peer-to-peer duplicate connect scenario, inbound and outbound paths do not carry symmetric usrpwd identity information:

• the accept path can learn the remote username
• the open path does not know the remote username and starts as unknown

Before this change, that difference leaked into transport compatibility and caused duplicate peer connections to be rejected with repeated OpenSyn -> Close(INVALID) errors.

Even if duplicate reconciliation succeeds, the authenticated principal still needs to be propagated to runtime interceptors, otherwise username-based ACL decisions may continue to observe stale metadata.

Related Issues

• Closes Repeated OpenSyn -> Close(INVALID) with usrpwd in a peer-to-peer duplicate connect scenario #2577
• Repro branch: https://github.com/BOURBONCASK/zenoh/tree/repro/usrpwd-duplicate-transport

Validation

• cargo test -p zenoh-transport --test unicast_authenticator --features transport_tcp,auth_usrpwd authenticator_tcp_usrpwd_peer_duplicate_transport -- --exact --nocapture
• cargo test -p zenoh --test authentication --features unstable test::test_authentication_usrpwd_duplicate_peer_acl_refresh -- --exact --nocapture
• cargo test -p zenoh --test authentication --features unstable test::test_authentication_usrpwd -- --exact --nocapture
• cargo test -p zenoh --test authentication --features unstable test::test_authentication_subject_combinations -- --exact --nocapture
• cargo check -p zenoh --features internal

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