p2p: fix dial scheduler and multichannel dial cleanup

[yoomee1313]

Proposed changes

This PR addresses p2p dial issues introduced by the DialSched refactor.

It contains three fixes:

063bb72 p2p: serialize dial candidate collection

• Fixes a dial scheduler race where getCandidates read scheduler bookkeeping across inconsistent lock snapshots.
• Keeps candidate demand calculation, static peer snapshot, dynamic queue refill, and CN allowlist filtering under one scheduler lock.
• This makes each dial candidate batch reflect one consistent view of connected/dialing/static/CN peer state.

b0690b2 p2p: preserve connected peers on dial failure

• Fixes a simultaneous dial case where outbound dial failure could remove bookkeeping for an already live inbound peer.
• markDialFailure now returns early when the peer is already present in connectedAll.
• This prevents failed outbound attempts from tearing down live peer accounting.

7fb2656 p2p: clean up incomplete multichannel dials

• Fixes partial multichannel dial cleanup when some channels succeed but the full peer is never assembled.
• dialMulti now verifies peer assembly after all channels, cleans only outbound pending candidates, and preserves inbound candidates from simultaneous dials.
• Incomplete multichannel dials no longer remove static peers, and the warning log includes expected/dialed/cleaned channel counts.

One known limitation remains: multichannel candidate assembly is still keyed only by peer ID, so inbound and outbound candidate state can share the same candidate set. This is an existing design limitation rather than a regression introduced by this PR, so it is left out of scope.

Types of changes

• 🐛 Bug fix
• ✨ Non-hardfork changes (node upgrade not required)
• 💥 Hardfork / consensus-breaking changes
• 🧪 Test improvements
• 🧰 CI / build tool
• ♻️ Chore / Refactor / Non-functional changes

Checklist

• 📖 I have read the CONTRIBUTING GUIDELINES doc
• 📝 I have signed in the PR comment I have read the CLA Document and I hereby sign the CLA in first time contribute after having read CLA
• 🟢 Lint and unit tests pass locally with my changes ($ make test)

Related issues

Further comments