[Fix] Prune old validator candidates

[ljedrz]

This PR extends the CandidatePeer with the last known Aleo address field, which is then used to prune the peer pool of outdated validator entries during the handshake, so that we don't attempt to reconnect to them again.

Small drive-bys:

• fix a Reconnnecting spelling error in a log (which may be an annoyance in debugging)
• moved a test block from the beginning of a module to its end (it threw me off when I was working on these changes)

Supersedes #4229.

Fixes #4228.

[Copilot]

Pull request overview

This PR improves peer pool hygiene by tracking a candidate peer’s last known Aleo address and using it during handshake to prune outdated validator candidate entries, reducing repeated reconnect attempts to stale IPs (related to #4228).

Changes:

• Extend CandidatePeer to include last_known_aleo_addr (carried over when a peer is downgraded from Connected → Candidate).
• Prune outdated candidate entries during Gateway handshake when the same Aleo address is observed from a different listening address.
• Small drive-bys: fix “Reconnnecting” log typo and move peering.rs tests to the end of the module.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
node/router/src/heartbeat.rs	Updates connection helper signature to use the now-generic CandidatePeer<N>.
node/network/src/peering.rs	Adjusts candidate-peer getters for CandidatePeer<N> and relocates the tests block.
node/network/src/peer.rs	Makes CandidatePeer network-generic and adds last_known_aleo_addr, populated on downgrade.
node/bft/src/gateway.rs	Fixes reconnect log typo and prunes outdated candidate entries during handshake using last_known_aleo_addr.

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[vicsn]

FYI I didn't merge due to the open copilot comments

[ljedrz]

@vicsn I replied to the leftover comments, feel free to proceed with merging if you agree.