Shrink persisted fork choice data (#7805)

Closes:

- https://github.com/sigp/lighthouse/issues/7760


  - [x] Remove `balances_cache` from `PersistedForkChoiceStore` (~65 MB saving on mainnet)
- [x] Remove `justified_balances` from `PersistedForkChoiceStore` (~16 MB saving on mainnet)
- [x] Remove `balances` from `ProtoArray`/`SszContainer`.
- [x] Implement zstd compression for votes
- [x] Fix bug in justified state usage
- [x] Bump schema version to V28 and implement migration.

beacon_node/beacon_chain/src/persisted_fork_choice.rs

@@ -1,16 +1,30 @@
-use crate::beacon_fork_choice_store::PersistedForkChoiceStoreV17;
+use crate::{
+    beacon_fork_choice_store::{PersistedForkChoiceStoreV17, PersistedForkChoiceStoreV28},
+    metrics,
+};
 use ssz::{Decode, Encode};
 use ssz_derive::{Decode, Encode};
-use store::{DBColumn, Error, StoreItem};
+use store::{DBColumn, Error, KeyValueStoreOp, StoreConfig, StoreItem};
 use superstruct::superstruct;
+use types::Hash256;
 
 // If adding a new version you should update this type alias and fix the breakages.
-pub type PersistedForkChoice = PersistedForkChoiceV17;
+pub type PersistedForkChoice = PersistedForkChoiceV28;
 
-#[superstruct(variants(V17), variant_attributes(derive(Encode, Decode)), no_enum)]
+#[superstruct(
+    variants(V17, V28),
+    variant_attributes(derive(Encode, Decode)),
+    no_enum
+)]
 pub struct PersistedForkChoice {
-    pub fork_choice: fork_choice::PersistedForkChoice,
-    pub fork_choice_store: PersistedForkChoiceStoreV17,
+    #[superstruct(only(V17))]
+    pub fork_choice_v17: fork_choice::PersistedForkChoiceV17,
+    #[superstruct(only(V28))]
+    pub fork_choice: fork_choice::PersistedForkChoiceV28,
+    #[superstruct(only(V17))]
+    pub fork_choice_store_v17: PersistedForkChoiceStoreV17,
+    #[superstruct(only(V28))]
+    pub fork_choice_store: PersistedForkChoiceStoreV28,
 }
 
 macro_rules! impl_store_item {
@@ -32,3 +46,35 @@ macro_rules! impl_store_item {
 }
 
 impl_store_item!(PersistedForkChoiceV17);
+
+impl PersistedForkChoiceV28 {
+    pub fn from_bytes(bytes: &[u8], store_config: &StoreConfig) -> Result<Self, Error> {
+        let decompressed_bytes = store_config
+            .decompress_bytes(bytes)
+            .map_err(Error::Compression)?;
+        Self::from_ssz_bytes(&decompressed_bytes).map_err(Into::into)
+    }
+
+    pub fn as_bytes(&self, store_config: &StoreConfig) -> Result<Vec<u8>, Error> {
+        let encode_timer = metrics::start_timer(&metrics::FORK_CHOICE_ENCODE_TIMES);
+        let ssz_bytes = self.as_ssz_bytes();
+        drop(encode_timer);
+
+        let _compress_timer = metrics::start_timer(&metrics::FORK_CHOICE_COMPRESS_TIMES);
+        store_config
+            .compress_bytes(&ssz_bytes)
+            .map_err(Error::Compression)
+    }
+
+    pub fn as_kv_store_op(
+        &self,
+        key: Hash256,
+        store_config: &StoreConfig,
+    ) -> Result<KeyValueStoreOp, Error> {
+        Ok(KeyValueStoreOp::PutKeyValue(
+            DBColumn::ForkChoice,
+            key.as_slice().to_vec(),
+            self.as_bytes(store_config)?,
+        ))
+    }
+}