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/manager.rs

@@ -198,8 +198,9 @@ pub enum BlockProcessType {
 impl BlockProcessType {
     pub fn id(&self) -> Id {
         match self {
-            BlockProcessType::SingleBlock { id } | BlockProcessType::SingleBlob { id } => *id,
-            BlockProcessType::SingleCustodyColumn(id)
+            BlockProcessType::SingleBlock { id }
+            | BlockProcessType::SingleBlob { id }
+            | BlockProcessType::SingleCustodyColumn(id)
             | BlockProcessType::SinglePayloadEnvelope(id) => *id,
         }
     }