numtide
types.paths.toType behavior for relative pathnames
Describe the bug
When using types.paths.toType with relative pathnames, the result might not be intuitive as paths will always be interpreted relative to /.
To Reproduce
E.g. let's imagine there is a file /tmp/test.nix that calls types.paths.toType "./derp", then the result will be /derp.
Expected behavior
For the above example, the user might reasonably assume the result to be /tmp/derp as that would correspond with way Nix treats paths.
Additional context
As there doesn't seem to be a way to capture the source file where the input string originates, it's probably better to add an assertion and only admit absolute pathnames here.
This issue was originally spotted at https://github.com/numtide/bld/pull/13/files#r1062709477
