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>