core/fetcher: fetch payload attestation data

[KaloyanTanev]

Add DutyPayloadAttestation support to the fetcher: fetch the versioned payload attestation data once per slot and fan it out to all PTC members in the definition set. A 204 from the beacon node (no block seen for the slot) is a plain, non-retryable error since there is nothing to attest.

category: feature
ticket: #4324

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

Adds Fetcher support for the Gloas Payload Timeliness Committee duty (DutyPayloadAttestation) by fetching per-slot payload attestation data from the beacon node once and fanning it out to all PTC members in the duty definition set. This integrates the new duty type into the existing core workflow “Fetcher → downstream subscribers” stage and aligns with the hardfork readiness work in #4324.

Changes:

• Adds a DutyPayloadAttestation case to Fetcher.Fetch and implements fetchPayloadAttestationData to query PayloadAttestationData for a slot and distribute the result to all definitions.
• Treats “no payload attestation data” (BN 204 / no block seen) as a non-retryable error with a clear message.
• Adds unit tests covering the happy path plus key error scenarios (no block, nil data, unsupported version).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
core/fetcher/fetcher.go	Adds payload attestation duty fetching and fan-out logic, including explicit handling for the “no block seen” case.
core/fetcher/fetcher_test.go	Adds tests validating per-slot fan-out semantics and error handling for payload attestation fetching.

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[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (gloas@6e58d4c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
core/fetcher/fetcher.go	90.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             gloas    #4667   +/-   ##
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  Coverage         ?   58.79%           
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  Files            ?      246           
  Lines            ?    34667           
  Branches         ?        0           
========================================
  Hits             ?    20383           
  Misses           ?    11752           
  Partials         ?     2532           

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