Adds blockhash to all ContractSendXXX events

def _add_blockhash_to_events(storage: SQLiteStorage, cache: BlockHashCache) -> None:
    """Adds blockhash to all ContractSendXXX events"""
    batch_query = storage.batch_query_event_records(
        batch_size=500,
        filters=[('_type', 'raiden.transfer.events.ContractSend%')],
    )
    for events_batch in batch_query:
        updated_events = []
        for event in events_batch:
            data = json.loads(event.data)
            assert 'triggered_by_block_hash' not in data, 'v18 events cant contain blockhash'
            # Get the state_change that triggered the event and get its hash
            matched_state_changes = storage.get_statechanges_by_identifier(
                from_identifier=event.state_change_identifier,
                to_identifier=event.state_change_identifier,
            )
            result_length = len(matched_state_changes)
            msg = 'multiple state changes should not exist for the same identifier'
            assert result_length == 1, msg

            statechange_data = json.loads(matched_state_changes[0])
            if 'block_hash' in statechange_data:
                data['triggered_by_block_hash'] = statechange_data['block_hash']
            elif 'block_number' in statechange_data:
                block_number = int(statechange_data['block_number'])
                data['triggered_by_block_hash'] = cache.get(block_number)

            updated_events.append((
                json.dumps(data),
                event.event_identifier,
            ))

        storage.update_events(updated_events)