Fixed a ton of state_processing stuff (#3642)

FIXME's:
 * consensus/fork_choice/src/fork_choice.rs
 * consensus/state_processing/src/per_epoch_processing/capella.rs
 * consensus/types/src/execution_payload_header.rs
 
TODO's:
 * consensus/state_processing/src/per_epoch_processing/capella/partial_withdrawals.rs
 * consensus/state_processing/src/per_epoch_processing/capella/full_withdrawals.rs

beacon_node/store/src/impls/execution_payload.rs

@@ -1,7 +1,35 @@
 use crate::{DBColumn, Error, StoreItem};
 use ssz::{Decode, Encode};
-use types::{EthSpec, ExecutionPayload};
+use types::{
+    EthSpec, ExecutionPayload, ExecutionPayloadCapella, ExecutionPayloadEip4844,
+    ExecutionPayloadMerge,
+};
 
+macro_rules! impl_store_item {
+    ($ty_name:ident) => {
+        impl<E: EthSpec> StoreItem for $ty_name<E> {
+            fn db_column() -> DBColumn {
+                DBColumn::ExecPayload
+            }
+
+            fn as_store_bytes(&self) -> Vec<u8> {
+                self.as_ssz_bytes()
+            }
+
+            fn from_store_bytes(bytes: &[u8]) -> Result<Self, Error> {
+                Ok(Self::from_ssz_bytes(bytes)?)
+            }
+        }
+    };
+}
+impl_store_item!(ExecutionPayloadMerge);
+impl_store_item!(ExecutionPayloadCapella);
+impl_store_item!(ExecutionPayloadEip4844);
+
+/// This fork-agnostic implementation should be only used for writing.
+///
+/// It is very inefficient at reading, and decoding the desired fork-specific variant is recommended
+/// instead.
 impl<E: EthSpec> StoreItem for ExecutionPayload<E> {
     fn db_column() -> DBColumn {
         DBColumn::ExecPayload
@@ -12,6 +40,13 @@ impl<E: EthSpec> StoreItem for ExecutionPayload<E> {
     }
 
     fn from_store_bytes(bytes: &[u8]) -> Result<Self, Error> {
-        Ok(Self::from_ssz_bytes(bytes)?)
+        ExecutionPayloadEip4844::from_ssz_bytes(bytes)
+            .map(Self::Eip4844)
+            .or_else(|_| {
+                ExecutionPayloadCapella::from_ssz_bytes(bytes)
+                    .map(Self::Capella)
+                    .or_else(|_| ExecutionPayloadMerge::from_ssz_bytes(bytes).map(Self::Merge))
+            })
+            .map_err(Into::into)
     }
 }