Update block_cache.rs

[oooLowNeoNooo]

Problem

The block cache consistency check only compared block numbers without verifying chain continuity. This could allow disconnected blocks to be added when the parent block wasn't in cache.

Solution

Updated the check to verify that new blocks actually continue the chain by validating:

• The block follows the finalized block (block_number == finalized_number + 1 with matching parent_hash)
• Or the block follows the latest cached block (block_number == latest_number + 1 with matching parent_hash)

Blocks that don't continue from any known block are now correctly rejected.