Fix electra light client types (#6361)

* 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

* fetch bootstrap without always querying for state

* storing bootstrap parts in db

* mroe code cleanup

* test

* prune sync committee branches from dropped chains

* 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

* resovle merge conflict

* add electra bootstrap logic, add logic to cache current sync committee

* add latest sync committe branch cache

* 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

* merge conflict

* add better error messaging

* resolve merge conflicts

* remove lc update from basicsim

* rename sync comittte variable and fix persist condition

* refactor get_light_client_update logic

* add better comments, return helpful error messages over http and rpc

* pruning canonical non checkpoint slots

* fix test

* rerun test

* update pruning logic, add tests

* fix tests

* fix imports

* fmt

* refactor db code

* Refactor db method

* Refactor db method

* lc electra changes

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

* add additional comments

* testing lc merkle changes

* lc electra

* update struct defs

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

* fix merge

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

* fix merge

* linting

* merge conflict

* prevent overflow

* enable lc server for http api tests

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

* get tests working:

* remove related TODOs

* fix test lint

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

* fix tests

* fix conflicts

* remove prints

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

* remove warning

* resolve conflicts

* merge conflicts

* linting

* remove comments

* cleanup

* linting

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

* pre/post electra light client cached data

* add proof type alias

* move is_empty_branch method out of impl

* add ssz tests for all forks

* refactor beacon state proof codepaths

* rename method

* fmt

* clean up proof logic

* refactor merkle proof api

* fmt

* Merge branch 'unstable' into light-client-electra

* Use superstruct mapping macros

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

* rename proof to merkleproof

* fmt

* Resolve merge conflicts

* merge conflicts

beacon_node/store/src/hot_cold_store.rs

@@ -44,7 +44,6 @@ use std::path::Path;
 use std::sync::Arc;
 use std::time::Duration;
 use types::data_column_sidecar::{ColumnIndex, DataColumnSidecar, DataColumnSidecarList};
-use types::light_client_update::CurrentSyncCommitteeProofLen;
 use types::*;
 
 /// On-disk database that stores finalized states efficiently.
@@ -641,15 +640,14 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
     pub fn get_sync_committee_branch(
         &self,
         block_root: &Hash256,
-    ) -> Result<Option<FixedVector<Hash256, CurrentSyncCommitteeProofLen>>, Error> {
+    ) -> Result<Option<MerkleProof>, Error> {
         let column = DBColumn::SyncCommitteeBranch;
 
         if let Some(bytes) = self
             .hot_db
             .get_bytes(column.into(), &block_root.as_ssz_bytes())?
         {
-            let sync_committee_branch: FixedVector<Hash256, CurrentSyncCommitteeProofLen> =
-                FixedVector::from_ssz_bytes(&bytes)?;
+            let sync_committee_branch = Vec::<Hash256>::from_ssz_bytes(&bytes)?;
             return Ok(Some(sync_committee_branch));
         }
 
@@ -677,7 +675,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
     pub fn store_sync_committee_branch(
         &self,
         block_root: Hash256,
-        sync_committee_branch: &FixedVector<Hash256, CurrentSyncCommitteeProofLen>,
+        sync_committee_branch: &MerkleProof,
     ) -> Result<(), Error> {
         let column = DBColumn::SyncCommitteeBranch;
         self.hot_db.put_bytes(