fix: get attester index from single attestation bytes if cache is used

[nflaig]

Motivation

As per discussion in #7260 we need to get the attester index from serialized bytes.

Currently we get the following error if cache entry is used

Nov-28 13:33:21.898[network]         debug: Gossip batch validation beacon_attestation threw a non-AttestationError - Cannot read properties of null (reading 'attesterIndex')
TypeError: Cannot read properties of null (reading 'attesterIndex')
    at validateAttestationNoSignatureCheck (file:///usr/app/packages/beacon-node/src/chain/validation/attestation.ts:426:93)
    at validateGossipAttestationsSameAttData (file:///usr/app/packages/beacon-node/src/chain/validation/attestation.ts:119:43)
    at Object.beacon_attestation (file:///usr/app/packages/beacon-node/src/network/processor/gossipHandlers.ts:625:64)
    at NetworkProcessor.gossipValidatorBatchFn (file:///usr/app/packages/beacon-node/src/network/processor/gossipValidatorFn.ts:36:75)
    at NetworkProcessor.processPendingGossipsubMessage (file:///usr/app/packages/beacon-node/src/network/processor/index.ts:438:20)
    at NetworkProcessor.executeWork (file:///usr/app/packages/beacon-node/src/network/processor/index.ts:398:16)
    at NetworkProcessor.pushPendingGossipsubMessageToQueue (file:///usr/app/packages/beacon-node/src/network/processor/index.ts:310:10)
    at NetworkProcessor.onPendingGossipsubMessage (file:///usr/app/packages/beacon-node/src/network/processor/index.ts:298:10)
    at NetworkEventBus.emit (node:events:520:28)

Description

Get attester index from single attestation bytes if cache is used

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 48.42%. Comparing base (cfe6c89) to head (5a665a5).
Report is 1 commits behind head on devnet-5.

Additional details and impacted files

@@             Coverage Diff              @@
##           devnet-5    #7264      +/-   ##
============================================
- Coverage     48.44%   48.42%   -0.02%     
============================================
  Files           602      602              
  Lines         40321    40331      +10     
  Branches       2057     2057              
============================================
  Hits          19532    19532              
- Misses        20751    20761      +10     
  Partials         38       38              

[twoeths]

lgtm