Cascading SWRCaches for stack info refresh

[lightwalker-eth]

See related discussion in Slack here: https://namehash.slack.com/archives/C086Z6FNBHN/p1778014729212909

Current idea to handle this in a mature way is for us to relax the constraint that each of the following are immutable for the lifetime of a process instance lifecycle once loaded:

• ENSIndexer's understanding of ENSRainbow's stack info
• ENSApi's understanding of ENSIndexer's stack info

For example, I imagine a mature solution to this could include:

• Transition each of the ideas listed above from being immutable once loaded, to being a SWR cache.
• Each time the SWR cache already has state X loaded and then refreshes it upon receiving a new value Y, logic should ensure no invariants are being broken by the new value Y. For example, that ENSRainbow hasn't changed from one label set id to another.

A nice benefit of this is that if someone running their own ENSNode instance does something creative where they significantly reconfigure their ENSRainbow mid-indexing process:

1. The label healing logic is already protected against this.
2. The next time the SWRCache inside ENSIndexer fetches the stack info from ENSRainbow it will identify the incompatibility at a deeper level and therefore might provide more helpful error info to the ENSNode operator / purposefully terminate itself.

[coderabbitai]

🔗 Related PRs

#1735 - ENSRainbow client graceful retry mechanism [merged]
#1843 - Onchain event handler preconditions [merged]

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