Fix stuck data column lookups by improving peer selection and retry logic (#8005)

Fixes the issue described in #7980 where Lighthouse repeatedly sends `DataColumnsByRoot` requests to the same peers that return empty responses, causing sync to get stuck.

The root cause was we don't count empty responses as failures, leading to excessive retries to unresponsive peers.


  - Track per peer attempts to limit retry attempts per peer (`MAX_CUSTODY_PEER_ATTEMPTS = 3`)
- Replaced random peer selection with hashing within each lookup to prevent splitting lookup into too many small requests and improve request batching efficiency.
- Added `single_block_lookup` root span to track all lookups created and added more debug logs:

<img width="1264" height="501" alt="image" src="https://github.com/user-attachments/assets/983629ba-b6d0-41cf-8e93-88a5b96c2f31" />


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

Co-Authored-By: Jimmy Chen <jimmy@sigmaprime.io>

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

@@ -384,6 +384,7 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
         // If we know that this lookup has unknown parent (is awaiting a parent lookup to resolve),
         // signal here to hold processing downloaded data.
         let mut lookup = SingleBlockLookup::new(block_root, peers, cx.next_id(), awaiting_parent);
+        let _guard = lookup.span.clone().entered();
 
         // Add block components to the new request
         if let Some(block_component) = block_component {