evn: improve node ID management with better error handling

[MatusKysel]

• Add proper error slice handling for txPool.Add operations
• Improve removal logic to only remove registered node IDs

[Copilot]

Pull Request Overview

This PR improves node ID management by adding proper error handling for txPool.Add operations and filtering node IDs for removal and addition based on their registration status.

• Retrieves registered node IDs and uses a lookup set for both removal and addition operations.
• Updates the error handling logic for adding transactions to the pool.

Comments suppressed due to low confidence (1)

eth/backend.go:621

• The diff uses 'addSet' in handleRemovals without providing its definition. Ensure that 'addSet' is properly initialized or passed as a parameter to avoid runtime errors.

if _, exists := addSet[id]; !exists {