sparse files size issue

[anshibanov]

First, I'd like to thank you for the prometheus_folder_size_exporter. It's been a valuable tool for our monitoring needs.

I've noticed that the current implementation reports the apparent (or nominal) size of files. While this might be useful in some contexts, it can lead to misleading metrics when dealing with sparse files. As you might know, the apparent size of a sparse file can be much larger than the actual disk space it uses.

To make the exporter more accurate for environments where sparse files are common, would it be possible to add an option or feature to report the actual disk space used by files, rather than their apparent size?

This would provide a more accurate picture of disk usage, especially when monitoring systems or applications that make use of sparse files.

Thank you for considering this feature request.