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/tests/lookups.rs

@@ -41,8 +41,8 @@ use slot_clock::{SlotClock, TestingSlotClock};
 use tokio::sync::mpsc;
 use tracing::info;
 use types::{
-    BeaconState, BeaconStateBase, BlobSidecar, DataColumnSidecar, EthSpec, ForkContext, ForkName,
-    Hash256, MinimalEthSpec as E, SignedBeaconBlock, Slot,
+    BeaconState, BeaconStateBase, BlobSidecar, BlockImportSource, DataColumnSidecar, EthSpec,
+    ForkContext, ForkName, Hash256, MinimalEthSpec as E, SignedBeaconBlock, Slot,
     data_column_sidecar::ColumnIndex,
     test_utils::{SeedableRng, TestRandom, XorShiftRng},
 };
@@ -1113,7 +1113,7 @@ impl TestRig {
         self.harness
             .chain
             .data_availability_checker
-            .put_pre_execution_block(block.canonical_root(), block)
+            .put_pre_execution_block(block.canonical_root(), block, BlockImportSource::Gossip)
             .unwrap();
     }