Merge sigp/unstable into gloas-lookup-sync-fixes

Brings in the gossip-blob deprecation (#9126) and 17 other unstable
commits. Conflict resolutions (8 files):

- Kept our unified `SyncMessage::UnknownParentSidecarHeader` design over
  unstable's separate `UnknownParentDataColumn`/`UnknownParentPartialDataColumn`
  variants (gossip_methods, manager, single_block_lookup, mod, tests).
- Adopted unstable's gossip-blob deprecation: dropped `process_gossip_blob`,
  `process_gossip_verified_blob`, and the blob parent-unknown test path.
- Took unstable's `process_gossip_verified_data_column` (Result-returning
  `to_partial`), router PayloadEnvelopesByRoot flattened match, and combined
  `BlockProcessType::id` arm.
- Dropped unstable's gloas-lookup-sync boilerplate stubs (#9322) that
  duplicated our real impls: `process_lookup_envelope`,
  `rpc_payload_envelope_received`, `on_single_payload_envelope_response`,
  and the `SinglePayloadEnvelope` processing-result arm.

cargo check -p network passes clean.

beacon_node/network/src/sync/block_lookups/mod.rs

@@ -203,9 +203,9 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
                 block_root,
                 Some(block_component),
                 Some(awaiting_parent),
-                // On a `UnknownParentBlock` or `UnknownParentBlob` event the peer is not required
-                // to have the rest of the block components (refer to decoupled blob gossip). Create
-                // the lookup with zero peers to house the block components.
+                // On a `UnknownParentBlock` or `UnknownParentSidecarHeader` event the peer is not
+                // required to have the rest of the block components (refer to decoupled blob
+                // gossip). Create the lookup with zero peers to house the block components.
                 &[],
                 &PeerType::PreGloas,
                 new_lookup_trigger,