fix: resend original WHOAREYOU during handshake retransmissions

[Gabriel-Trintinalia]

When a session is in WHOAREYOU_SENT and another unauthorised packet arrives (e.g. a retransmission), we were generating a new WHOAREYOU with a fresh nonce.

That breaks the handshake: the initiator has already signed against the original challenge, so the next HANDSHAKE gets rejected.

This change reuses the original WHOAREYOU instead of creating a new one, keeping the challenge stable and the handshake valid.

The spec requires this behaviour:

▎ If the recipient has already sent a WHOAREYOU for the node, it should re-send the same WHOAREYOU packet.

• Fix HandshakeResend hive test

---

Note

Medium Risk
Touches session-handshake state and packet emission behavior; incorrect handling could break peer session establishment or cause stuck handshakes under packet loss/retransmit scenarios.

Overview
Ensures UnauthorizedMessagePacketHandler does not generate a new WHOAREYOU when the session is already in WHOAREYOU_SENT, and instead triggers a resend of the original challenge.

Adds NodeSession tracking for the last outbound WhoAreYouPacket plus a resendOutgoingWhoAreYou() path that reuses the original masking IV/challenge bytes, and clears the pending packet when the handshake state is reset. Updates/extends tests to cover the resend behavior and challenge stability.

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[macfarla]

LGTM