Prysm v7.1.5 Ships Gloas ePBS Fork Work

Prysm v7.1.5 released June 16, 2026, dominated by Gloas (ePBS) fork development. Adds EIP-8045, payload attestation duties, execution payload envelope endpoints, and Gloas-aware fork-choice dump. Streams validator lists instead of materializing ~2.3M validators, enabling O(1) builder lookups. Client code changed to PM. Updated to Go 1.26.4 and go-libp2p v0.44.0. No known security issues.