Support Fulu data columns and Gloas gossip topic forwarding

[swarna1101]

Context

GloasForkEpoch is still disabled on mainnet and Hoodi today, so there is no production impact yet. The gateway currently bridges only beacon_block and beacon_attestation_* gossip topics.

data_column_sidecar_* topic descriptor validation already exists in pkg/entities/eth_topics.go, but those topics are not subscribed or forwarded.

Scope

1. Fulu - data_column_sidecar_* forwarding

• Subscribe, validate, and bridge CL ↔ mump2p for data column sidecar topics
• Extend TopicMeta / topic filters beyond blocks + attestations
• Decide aggregation strategy (raw forward vs pack, per column index)
• Validation should follow consensus spec SSZ rules, not a single client implementation

2. Gloas - new gossip topics

Topic	SSZ type
payload_attestation_message	PayloadAttestationMessage
execution_payload_bid	SignedExecutionPayloadBid
proposer_preferences	SignedProposerPreferences
execution_payload_envelope	SignedExecutionPayloadEnvelope
beacon_block	SignedBeaconBlockGloas

• Add topic descriptors, subscription wiring, and CL <-> mump2p bridging for each
• Gate activation on fork epoch configuration

3. Gloas attestation fast-path

• Review ParseAttestationSSZTopic byte-offset parsing - Gloas changes attestation index semantics per the spec
• Ensure subnet routing and aggregation remain correct post-fork

Non-goals

• No client-specific validation logic copied from a single CL codebase
• No production enablement until fork epochs are scheduled on target networks

Acceptance

• Topic list and filters cover Fulu data columns and Gloas gossip where the gateway is active
• Hoodi (or fork testnet) smoke test confirms subscribe + forward without breaking existing block/attestation paths
• Fork gating documented in config / release notes