Added version field to gloas events

[rolfyone]

Implements change in
ethereum/beacon-APIs#587

If any devnet0 watchers are looking at these, this is non-compatible.

Fixed Issue(s)

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

Medium Risk
Changes the JSON shape of execution_payload_bid and payload_attestation_message SSE payloads by wrapping existing data with a version field, which is a client-visible (potentially breaking) API change.

Overview
Adds a version field to Gloas-specific SSE events. The execution_payload_bid and payload_attestation_message event payloads are now emitted as an object containing {version, data} instead of the raw message/bid, using MILESTONE_TYPE and SpecMilestone.GLOAS.

Tests are updated to assert the serialized SSE output includes "version":"gloas" for both event types.

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