- Refactor `RODataColumn` to support both Fulu and Gloas data column
sidecar protobuf types. Fulu-only accessors now return errors instead of
zero values when called on Gloas sidecars
- Wire up Gloas `DataColumnSidecarGloas` across gossip topic mappings,
pubsub decoding, validation, and RPC serving
- Gloas duplicate check uses `(block_root, index)` per spec
- Precompute and broadcast Gloas data column sidecars during block
proposal, before the execution payload envelope, so receivers pass data
availability checks
- Fix `WriteDataColumnSidecarChunk` to encode the correct SSZ type per
fork