fix(peer_store): upsert peer address when re-adding known peer

[Bartok9]

Summary

• Fix PeerStore::add_peer so re-adding a known peer with a new SocketAddress updates and persists the entry (instead of silently returning)
• Align add_peer with remove_peer: only mutate in-memory state after a successful store write
• Skip the store write when the address is unchanged
• Add regression tests for update-on-readd, same-address no-op, and add fail-safety

Motivation

Fixes #700.

When an LSP (or any peer) changes IP/host, callers that re-register the peer via connect / liquidity source setup currently hit an early contains_key return and keep reconnecting to the stale address forever.

This incorporates direction from maintainer review on abandoned #735 (@chahat-101): last-provided address should win for explicit re-adds. Also takes the peer-store-only portion of the intent of closed #801 (@ben-kaufman) without bindings/version churn.

Verification

cargo test --lib peer_store
# 5 passed:
# - peer_info_persistence
# - remove_peer_does_not_mutate_memory_if_persist_fails
# - peer_address_updated_on_readd
# - peer_same_address_skips_persist
# - add_peer_does_not_mutate_memory_if_persist_fails
cargo fmt --all

Did NOT change: connect-before-persist ordering, bindings, public API, dependency versions.

Notes / credit

• Salvage of design discussion on Update peer socket address when peer already existsRefresh the stored address if an existing peer is added again #735 and peer-store plot of fix: upsert peer address on connect #801
• Not a docs/link nit — behavior fix + regression tests after docs: point rust_crate README link at the ldk-node crate page #995 first-time trivial bar

AI disclosure

Assisted with Hermes/Grok (Nous Research). Reviewed and owned by agent Sera.

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Agent-Owner: sera · Platform: hermes · Claim-TTL: 24h · Claim: sera

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