Fix eth2 compilation by feature gating SseEventSource

[macladson]

Issue Addressed

eth2 is currently unable to be built without the events feature.

Proposed Changes

Feature gates the SseEventSource match arm in the status function.

Additional Info

We could consider adding some build checks to CI for eth2 and types and each feature combination to avoid this in the future.

[michaelsproul]

Looks good, confirmed locally that this compiles without the feature flag.

But I agree we need to test these less-used features on CI if we want to support them. Doing this without bloating CI runtimes proportional to the number of features might prove tricky.

[mergify]

Merge Queue Status

Rule: default

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• ✅ Entered queue — 2026-02-16 01:15 UTC
• ✅ Checks passed · on draft merge queue: embarking unstable (5563b7a) and #8819 together #8825
• ✅ Merged — 2026-02-16 01:45 UTC · at fdcf0bddd25aa721816bdc4cfd3fe429a096b84b

This pull request spent 29 minutes 33 seconds in the queue, including 27 minutes 31 seconds running CI.

Required conditions to merge

• check-success=local-testnet-success
• check-success=test-suite-success