Capella consensus review (#4012)

* Add extra encoding/decoding tests

* Remove TODO

The method LGTM

* Remove `FreeAttestation`

This is an ancient relic, I'm surprised it still existed!

* Add paranoid check for eip4844 code

This is not technically necessary, but I think it's nice to be explicit about
EIP4844 consensus code for the time being.

* Reduce big-O complexity of address change pruning

I'm not sure this is *actually* useful, but it might come in handy if we see a
ton of address changes at the fork boundary. I know the devops team have been
testing with ~100k changes, so maybe this will help in that case.

* Revert "Reduce big-O complexity of address change pruning"

This reverts commit e7d93e6cc7.

consensus/state_processing/src/per_block_processing.rs

@@ -180,7 +180,11 @@ pub fn per_block_processing<T: EthSpec, Payload: AbstractExecPayload<T>>(
         )?;
     }
 
-    process_blob_kzg_commitments(block.body())?;
+    // Eip4844 specifications are not yet released so additional care is taken
+    // to ensure the code does not run in production.
+    if matches!(block, BeaconBlockRef::Eip4844(_)) {
+        process_blob_kzg_commitments(block.body())?;
+    }
 
     Ok(())
 }