fix: correct block hash validation in get_payloads function

[avorylli]

The get_payloads function was comparing block_hash() with prev_parent_hash, which is incorrect for validating block chain consistency. Changed to compare parent_hash() with prev_parent_hash to ensure proper block linking.

Impact:

• Fixes potential block synchronization issues
• Ensures correct block chain validation
• Prevents false-positive chain breaks

[ncitron]

This function is correct as is. The parent hash of block n must be equal to the block hash of block n-1. This change would cause all calls to get_payloads to fail since it would check that the parent hash of block n is equal to the parent hash of block n-1, which it will never be.