Consolidate reqresp_pre_import_cache into data_availability_checker (#8045)

This PR consolidates the `reqresp_pre_import_cache` into the `data_availability_checker` for the following reasons:
- the `reqresp_pre_import_cache` suffers from the same TOCTOU bug we had with `data_availability_checker` earlier, and leads to unbounded memory leak, which we have observed over the last 6 months on some nodes.
- the `reqresp_pre_import_cache` is no longer necessary, because we now hold blocks in the `data_availability_checker` for longer since (#7961), and recent blocks can be served from the DA checker.

This PR also maintains the following functionalities
- Serving pre-executed blocks over RPC, and they're now served from the `data_availability_checker` instead.
- Using the cache for de-duplicating lookup requests.


  


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

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

beacon_node/beacon_chain/src/builder.rs

@@ -998,7 +998,6 @@ where
             validator_pubkey_cache: RwLock::new(validator_pubkey_cache),
             attester_cache: <_>::default(),
             early_attester_cache: <_>::default(),
-            reqresp_pre_import_cache: <_>::default(),
             light_client_server_cache: LightClientServerCache::new(),
             light_client_server_tx: self.light_client_server_tx,
             shutdown_sender: self