feat: Load from .SRCINFO
This adds a function to load package info from a .SRCINFO
file using python-srcinfo.
The first unit test is rather ugly, because it needs normalization on the object created by load_from_pkgbuild
before comparing the result of the new function. But it shows some potential issues that will need to be solved when migrating to .SRCINFO
in the whole codebase.
Related to #91