Memory usage reduction (#1522)

## Issue Addressed

NA

## Proposed Changes

- Adds a new function to allow getting a state with a bad state root history for attestation verification. This reduces unnecessary tree hashing during attestation processing, which accounted for 23% of memory allocations (by bytes) in a recent `heaptrack` observation.
- Don't clone caches on intermediate epoch-boundary states during block processing.
- Reject blocks that are known to fork choice earlier during gossip processing, instead of waiting until after state has been loaded (this only happens in edge-case).
- Avoid multiple re-allocations by creating a "forced" exact size iterator.

## Additional Info

NA

beacon_node/beacon_chain/src/attestation_verification.rs

@@ -775,7 +775,12 @@ where
             metrics::start_timer(&metrics::ATTESTATION_PROCESSING_STATE_READ_TIMES);
 
         let mut state = chain
-            .get_state(&target_block.state_root, Some(target_block.slot))?
+            .store
+            .get_inconsistent_state_for_attestation_verification_only(
+                &target_block.state_root,
+                Some(target_block.slot),
+            )
+            .map_err(BeaconChainError::from)?
             .ok_or_else(|| BeaconChainError::MissingBeaconState(target_block.state_root))?;
 
         metrics::stop_timer(state_read_timer);