ValueFormat::text_formatter is called with a u64 retrieved from
GraphWidget::m_values. However, the function pointer definition used
size_t and all the users of text_formatter used int. If bytes was over
~2 billion, we would interpret bytes to be negative. We then pass this
into `human_readable_size` which converts it to a u64, making it out to
be about 15.9 EiB.
This is fixed by making everything in the path take a u64.