feat: add sunsetAt datetime for chains

[simsonraj]

Add sunset dates for deprecated chains

Deprecation vs. sunset: Deprecated marks a chain as discouraged (it may still be live).
SunsetAt is the date it goes offline — a future date means it is still live, a past date
means it is offline. Empty means no sunset is scheduled.

Summary

• Introduces a sunset_at field to track when a chain went (or will go) offline, and backfills it for deprecated chains using researched shutdown dates.
• marks all remaining Goerli-based testnets as deprecated.
• Previously we only had a boolean deprecated flag with no notion of when — this enables downstream systems (e.g. Insights, alerting) to build advance-warning logic and distinguish "deprecated" from "actually offline".

Changes

New API (types.go, selectors.go)

• ChainDetails.SunsetAt — optional RFC 3339 datetime or 2006-01-02 date; empty means no sunset set. Fully backward compatible (omitempty).
• GetSunsetDate(selector) (time.Time, bool, error) — returns the parsed date; ok is false when none is set.
• IsSunset(selector) (bool, error) — reports whether the sunset date has passed as of now.
• IsDeprecated is unchanged.

Data (selectors.yml, regenerated all_selectors.yml)

• Backfilled sunset_at on 47 deprecated chains with dates sourced from official announcements / block explorers.
• Marked 6 Goerli testnets (goerli-{arbitrum,base,linea,mantle,optimism,zksync}-1) as deprecated with Goerli's sunset date (2024-04-13).
• All Holesky chains carry 2025-09-30 (Ethereum Holesky sunset), except holesky-fraxtal-1 (2025-10-17) and holesky-morph-1 (2025-10-21), which keep their own confirmed shutdown dates.

[github-actions]

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[Copilot]

Pull request overview

Adds a sunset_at timestamp to chain metadata so downstream consumers can distinguish “deprecated” from “actually offline,” and provides Go helpers (local + remote) to parse and evaluate that sunset date.

Changes:

• Extends ChainDetails with optional SunsetAt (sunset_at in YAML).
• Adds parsing/accessor helpers: ParseSunsetDate, GetSunsetDate, SunsetPassed, IsSunset (+ remote equivalents).
• Backfills sunset_at for deprecated chains and adds tests to ensure all configured dates parse.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
types.go	Adds SunsetAt to ChainDetails.
selectors.go	Implements sunset parsing and “has sunset passed” helpers.
selectors_test.go	Adds unit tests for parsing and sunset logic + validates all configured sunset_at values.
remote/remote.go	Adds remote API equivalents for sunset helpers.
selectors.yml	Backfills sunset_at values and deprecates remaining Goerli testnets per PR description.
all_selectors.yml	Regenerated output including sunset_at fields.
test_extra_selectors.yml	Adds an extra-selector fixture with a past sunset_at.
extra_selectors_test.go	Extends E2E test to validate sunset_at propagation.
README.md	Documents the new sunset helpers and explains “deprecation vs. sunset.”

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