improve(svm): extract code/wasClean from Solana WS close and route log level

[droplet-rl]

Summary

The reconnect-on-close warn introduced in #3417 logs the raw SolanaError.cause, which is a Node CloseEvent. CloseEvent exposes code, wasClean, and reason as prototype getters, so winston serializes the cause as {} (Cloud Logging) or "[object CloseEvent]" (winston transport) and the only useful fields are dropped. Slack sees them only because its formatter walks the prototype — which is also why we get the giant initEvent/stopImmediatePropagation/etc dump in the Slack message.

This change projects the three scalars (code, wasClean, reason) onto own properties before logging, drops the rest of the CloseEvent, and routes the log level on the extracted signal:

• code === 1006 && wasClean === false → debug. This is the documented Chainstack shared-gateway rotation at a wallclock 10-min cadence and is operational noise.
• Anything else (notably code: 1011, wasClean: true, reason: "Internal Error" from Alchemy, plus unknown codes) → warn, unchanged.

Empirical justification (bots-across-3839, 7 days 2026-05-21 → 2026-05-28, both primary + usdh):

	Alchemy	Chainstack
code: 1011, wasClean: true	2922	0
code: 1006, wasClean: false	11	305

So 1006-vs-1011 is essentially a clean per-provider split: Chainstack 1006 is the wallclock-rotation noise we already know about; Alchemy 1011 is the current high-volume signal (~417/day/bot) and stays at warn so it remains alertable. The full structured log now looks like:

{
  "at": "RelayerSpokePoolListenerSVM::listen",
  "message": "Caught error on Solana provider; reconnecting.",
  "provider": "wss://solana-mainnet.g.alchemy.com",
  "backoffS": 1,
  "code": 1011,
  "wasClean": true,
  "reason": "Internal Error"
}

…instead of the previous cause: {} (GCP) or full CloseEvent dump (Slack).

Test plan

• yarn tsc --noEmit clean
• yarn eslint clean on changed file
• yarn prettier --check clean on changed file
• No runtime test — the helper is straightforward field projection of a 3-field shape, and the routing is one ternary. Happy to add a unit test if preferred.
• After merge: 1006-Chainstack-noise should disappear from #zbot-across-relayer-* Slack channels; 1011-Alchemy warns should continue to appear, now structured rather than dumped.

🤖 Generated with Claude Code

[droplet-rl]

Thanks for the approval. The review (pullrequestreview-4380525321) is a plain approve — empty body and no inline comments — and the PR merged ~30s later (2864baa5), so there's no feedback to address and nothing to push.