fix nil pointer panic in check_consensus_sync_status

[yperbasis]

Summary

• Fix nil pointer dereference in check_consensus_sync_status when GetNodeSyncStatus returns an error
• When the RPC call fails (e.g. during network bootstrap before genesis), syncStatus is nil, but getClientInfo dereferences it unconditionally — causing a panic
• The analogous check_execution_sync_status task already has this nil guard; this applies the same pattern

Panic trace from CI

panic: runtime error: invalid memory address or nil pointer dereference

goroutine 172 [running]:
github.com/ethpandaops/assertoor/pkg/tasks/check_consensus_sync_status.(*Task).getClientInfo(...)
    pkg/tasks/check_consensus_sync_status/task.go:219
github.com/ethpandaops/assertoor/pkg/tasks/check_consensus_sync_status.(*Task).processCheck(...)
    pkg/tasks/check_consensus_sync_status/task.go:142

Observed in Erigon CI glamsterdam Kurtosis tests: https://github.com/erigontech/erigon/actions/runs/24228480466/job/70734695754

Test plan

• Verify check_consensus_sync_status no longer panics when a CL client is unreachable during startup
• Verify ClientInfo for failed clients has Name populated and sync fields zeroed

[qu0b]

Consider setting variables explicitly rather than letting golang use defaults here:

       if syncStatus == nil {                                                                                                                                                                                                                                   
           // RPC failed - return skeletal info without dereferencing                                                                                                                                                                                           
           return &ClientInfo{                                                                                                                                                                                                                                  
               Name:          client.Config.Name,                                                                                                                                                                                                               
               Synchronizing: true,  // Sentinel: we don't know, assume unhealthy                                                                                                                                                                               
               SyncHead:      0,                                                                                                                                                                                                                                
               SyncDistance:  0,                                                                                                                                                                                                                                
           }                                                                                                                                                                                                                                                    
       }