Only mark block lookups as pending if block is importing from gossip (#8112)

- PR https://github.com/sigp/lighthouse/pull/8045 introduced a regression of how lookup sync interacts with the da_checker.

Now in unstable block import from the HTTP API also insert the block in the da_checker while the block is being execution verified. If lookup sync finds the block in the da_checker in `NotValidated` state it expects a `GossipBlockProcessResult` message sometime later. That message is only sent after block import in gossip.

I confirmed in our node's logs for 4/4 cases of stuck lookups are caused by this sequence of events:
- Receive block through API, insert into da_checker in fn process_block in put_pre_execution_block
- Create lookup and leave in AwaitingDownload(block in processing cache) state
- Block from HTTP API finishes importing
- Lookup is left stuck

Closes https://github.com/sigp/lighthouse/issues/8104


  - https://github.com/sigp/lighthouse/pull/8110 was my initial solution attempt but we can't send the `GossipBlockProcessResult` event from the `http_api` crate without adding new channels, which seems messy.

For a given node it's rare that a lookup is created at the same time that a block is being published. This PR solves https://github.com/sigp/lighthouse/issues/8104 by allowing lookup sync to import the block twice in that case.


Co-Authored-By: dapplion <35266934+dapplion@users.noreply.github.com>

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

@@ -219,7 +219,7 @@ impl<T: BeaconChainTypes> SingleBlockLookup<T> {
                 // can assert that this is the correct value of `blob_kzg_commitments_count`.
                 match cx.chain.get_block_process_status(&self.block_root) {
                     BlockProcessStatus::Unknown => None,
-                    BlockProcessStatus::NotValidated(block)
+                    BlockProcessStatus::NotValidated(block, _)
                     | BlockProcessStatus::ExecutionValidated(block) => Some(block.clone()),
                 }
             }) {