Fix: signer identity validation for signed PeerRecords

[sumanjeet0012]

What was wrong?

Fixes #1338

KadDHT accepted signed PeerRecords where the signer identity did not match record.peer_id.

Although the envelope signature was valid, the signer public key embedded in the envelope could derive to a different peer ID than the one claimed in the record payload.

This allowed authenticated but incorrectly bound peer records to poison the certified address book for arbitrary peer IDs.

How was it fixed?

Added signer identity binding validation before accepting signed peer records.

The fix enforces:

signer_peer_id = ID.from_pubkey(envelope.public_key)

Records with mismatched signer identities are now rejected before they can update certified peer addresses.

To-Do

• Clean up commit history
• Add or update documentation related to these changes
• Add entry to the release notes

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