Refactor consensus/types (#7827)

Organize and categorize `consensus/types` into modules based on their relation to key consensus structures/concepts.
This is a precursor to a sensible public interface.

While this refactor is very opinionated, I am open to suggestions on module names, or type groupings if my current ones are inappropriate.


Co-Authored-By: Mac L <mjladson@pm.me>

beacon_node/beacon_chain/src/attester_cache.rs

@@ -17,7 +17,7 @@ use std::ops::Range;
 use types::{
     BeaconState, BeaconStateError, ChainSpec, Checkpoint, Epoch, EthSpec, FixedBytesExtended,
     Hash256, RelativeEpoch, Slot,
-    attestation::Error as AttestationError,
+    attestation::AttestationError,
     beacon_state::{
         compute_committee_index_in_epoch, compute_committee_range_in_epoch, epoch_committee_count,
     },