These are sent out for all txs in a block after Avalanche finalized a block.
Unlike `handle_block_connected` and `handle_block_disconnected`, we don't get the txs in `handle_block_finalized`, therefore we have to load them from disk.
Note: In protobuf, all entries in an enum share the same namespace, which is why we have to name it `TX_FINALIZED` and not `FINALIZED`, as that would clash with `BlockMsgType`.