Research and implement Beacon Chain API endpoints

[LeoPatOZ]

Summary

The Robust Provider currently only supports execution layer RPC methods. Beacon Chain (consensus layer) API endpoints are not supported.

Problem

Users interacting with the consensus layer cannot benefit from the retry/fallback mechanisms that Robust Provider offers.

Proposed Solution

• Research the Beacon API spec
• Determine which endpoints are most commonly used and should be prioritized
• Evaluate whether beacon endpoints fit the current architecture or require restructuring (e.g., separating by namespace)
• Implement priority endpoints with retry/fallback support
• Add tests

Open Questions

• Should beacon endpoints live in the same crate or a separate feature flag?
• How do we handle the different base URL (beacon node vs execution node)?