added an executor for Gossip beacon attestation reftests

[rolfyone]

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

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Note

Low Risk
Low risk: changes are confined to eth reference-test harnesses, enabling a previously ignored gossip attestation test type and adding validation scaffolding.

Overview
Adds a new GossipBeaconAttestationTestExecutor that runs networking/gossip_beacon_attestation reftests by building an in-memory chain/fork-choice context, importing provided blocks, and validating each attestation against expected valid/reject/ignore outcomes (including duplicate and failed-block cases).

Updates GossipTests to execute these tests instead of marking them as IGNORE_TESTS.

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[tbenr]

I'd just move the seenAttestationRoots.add regardless the validation result

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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