Persist light client updates (#5545)

* persist light client updates

* update beacon chain to serve light client updates

* resolve todos

* cache best update

* extend cache parts

* is better light client update

* resolve merge conflict

* initial api changes

* add lc update db column

* fmt

* added tests

* add sim

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates

* fix some weird issues with the simulator

* tests

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates

* test changes

* merge conflict

* testing

* started work on ef tests and some code clean up

* update tests

* linting

* noop pre altair, were still failing on electra though

* allow for zeroed light client header

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates

* merge unstable

* remove unwraps

* remove unwraps

* Update light_client_update.rs

* merge unstable

* move functionality to helper methods

* refactor is best update fn

* refactor is best update fn

* improve organization of light client server cache logic

* fork diget calc, and only spawn as many blcoks as we need for the lc update test

* fetch lc update from the cache if it exists

* fmt

* Fix beacon_chain tests

* Add debug code to update ranking_order ef test

* Fix compare code

* merge conflicts

* fix test

* Merge branch 'persist-light-client-updates' of https://github.com/eserilev/lighthouse into persist-light-client-updates

* Use blinded blocks for light client proofs

* fix ef test

* merge conflicts

* fix lc update check

* Lint

* resolve merge conflict

* Merge branch 'persist-light-client-updates' of https://github.com/eserilev/lighthouse into persist-light-client-updates

* revert basic sim

* small fix

* revert sim

* Review PR

* resolve merge conflicts

* Merge branch 'unstable' into persist-light-client-updates

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -1351,14 +1351,27 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     ) -> Result<(), Error> {
         self.light_client_server_cache.recompute_and_cache_updates(
             self.store.clone(),
-            &parent_root,
             slot,
+            &parent_root,
             &sync_aggregate,
             &self.log,
             &self.spec,
         )
     }
 
+    pub fn get_light_client_updates(
+        &self,
+        sync_committee_period: u64,
+        count: u64,
+    ) -> Result<Vec<LightClientUpdate<T::EthSpec>>, Error> {
+        self.light_client_server_cache.get_light_client_updates(
+            &self.store,
+            sync_committee_period,
+            count,
+            &self.spec,
+        )
+    }
+
     /// Returns the current heads of the `BeaconChain`. For the canonical head, see `Self::head`.
     ///
     /// Returns `(block_root, block_slot)`.