superstruct the AttesterSlashing (#5636)

* `superstruct` Attester Fork Variants

* Push a little further

* Deal with Encode / Decode of AttesterSlashing

* not so sure about this..

* Stop Encode/Decode Bounds from Propagating Out

* Tons of Changes..

* More Conversions to AttestationRef

* Add AsReference trait (#15)

* Add AsReference trait

* Fix some snafus

* Got it Compiling! :D

* Got Tests Building

* Get beacon chain tests compiling

---------

Co-authored-by: Michael Sproul <micsproul@gmail.com>

testing/ef_tests/src/cases/operations.rs

@@ -93,7 +93,7 @@ impl<E: EthSpec> Operation<E> for Attestation<E> {
         match state {
             BeaconState::Base(_) => base::process_attestations(
                 state,
-                &[self.clone()],
+                [self.clone().to_ref()].into_iter(),
                 VerifySignatures::True,
                 &mut ctxt,
                 spec,
@@ -106,7 +106,7 @@ impl<E: EthSpec> Operation<E> for Attestation<E> {
                 initialize_progressive_balances_cache(state, spec)?;
                 altair_deneb::process_attestation(
                     state,
-                    self,
+                    self.to_ref(),
                     0,
                     &mut ctxt,
                     VerifySignatures::True,
@@ -123,7 +123,7 @@ impl<E: EthSpec> Operation<E> for AttesterSlashing<E> {
     }
 
     fn decode(path: &Path, _fork_name: ForkName, _spec: &ChainSpec) -> Result<Self, Error> {
-        ssz_decode_file(path)
+        Ok(Self::Base(ssz_decode_file(path)?))
     }
 
     fn apply_to(
@@ -136,7 +136,7 @@ impl<E: EthSpec> Operation<E> for AttesterSlashing<E> {
         initialize_progressive_balances_cache(state, spec)?;
         process_attester_slashings(
             state,
-            &[self.clone()],
+            [self.clone().to_ref()].into_iter(),
             VerifySignatures::True,
             &mut ctxt,
             spec,