Implement Overflow LRU Cache for Pending Blobs (#4203)

* All Necessary Objects Implement Encode/Decode

* Major Components for LRUOverflowCache Implemented

* Finish Database Code

* Add Maintenance Methods

* Added Maintenance Service

* Persist Blobs on Shutdown / Reload on Startup

* Address Clippy Complaints

* Add (emum_behaviour = "tag") to ssz_derive

* Convert Encode/Decode Implementations to "tag"

* Started Adding Tests

* Added a ton of tests

* 1 character fix

* Feature Guard Minimal Spec Tests

* Update beacon_node/beacon_chain/src/data_availability_checker.rs

Co-authored-by: realbigsean <seananderson33@GMAIL.com>

* Address Sean's Comments

* Add iter_raw_keys method

* Remove TODOs

---------

Co-authored-by: realbigsean <seananderson33@GMAIL.com>

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -465,7 +465,7 @@ pub struct BeaconChain<T: BeaconChainTypes> {
     /// Provides monitoring of a set of explicitly defined validators.
     pub validator_monitor: RwLock<ValidatorMonitor<T::EthSpec>>,
     pub proposal_blob_cache: BlobCache<T::EthSpec>,
-    pub data_availability_checker: DataAvailabilityChecker<T::EthSpec, T::SlotClock>,
+    pub data_availability_checker: DataAvailabilityChecker<T>,
     pub kzg: Option<Arc<Kzg>>,
 }
 
@@ -609,6 +609,13 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         Ok(())
     }
 
+    pub fn persist_data_availabilty_checker(&self) -> Result<(), Error> {
+        let _timer = metrics::start_timer(&metrics::PERSIST_DATA_AVAILABILITY_CHECKER);
+        self.data_availability_checker.persist_all()?;
+
+        Ok(())
+    }
+
     /// Returns the slot _right now_ according to `self.slot_clock`. Returns `Err` if the slot is
     /// unavailable.
     ///
@@ -6268,6 +6275,7 @@ impl<T: BeaconChainTypes> Drop for BeaconChain<T> {
         let drop = || -> Result<(), Error> {
             self.persist_head_and_fork_choice()?;
             self.persist_op_pool()?;
+            self.persist_data_availabilty_checker()?;
             self.persist_eth1_cache()
         };