HaikuDepot: Size Package Files

Obtain the size of local package files.

Fixes #17445

Change-Id: Ica15d3f7c1e80bcf9b3b23d6af851cc33b5b6253
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5016
Reviewed-by: Andrew Lindesay <apl@lindesay.co.nz>

HaikuDepot: Background Processing

Unify the background processing in the
application to one system and refactor
the package actions. This won't fix
any specific current issues with this
area, but lays the ground for later
fixes.

Change-Id: I098b81e7afc4aeb883bddf1acfc01f7888134257
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3997
Reviewed-by: Andrew Lindesay <apl@lindesay.co.nz>