feat: move PhysicalPageFlags to procfs-core

[tatref]

Hi,

I needed to use PhysicalPageFlags for a Windows project, so I moved it to procfs-core

I made parse_info pub

I removed the import of CGroupController to remove a warning

Maybe we could move KPageFlags also, but we would need to also move FileWrapper that is part of procfs.
What do you think?

[eminence]

Regarding KPageFlags, we could maybe move the from_custom_root into some trait that only exists in procfs (not procfs-core).

I need to review how procfs types are constructed in general, but I think we aren't very consistent. For example, I think several types should impl Current but don't at the moment