How do I import both the unmodified original and current edits versions of photos to a new Photos Library?

You will have to export the unmodified originals, and also the edited versions. Use both export options.

You can search for all photos that have edits applied with a smart album with the rule "Photo is edited".

Then import both the edited version and the originals to the new library. You will then see two files for each edited image in your library. These duplicates cannot be prevented.

If you want to move many images to a new library, it would be more economic to duplicate the library and to delete all photos you do not want to move to the new library. this way the originals and the edited versions will remain paired. It is the best, lossless method.

For RAW images is a nearly lossless way to transfer the edited versions and the RAW files as a RAW&JPEG pair, so you will not see duplicates after importing them. If your original image files are RAW files, and you export the edited versions as JPEGS and the originals as RAW files, and use the original filename when exporting, Photos will combine the edited version and the original RAW file as a RAW&JPEG pair, when you import the two files together to Photos. Photos will use the JPEG of the edited pair as the original file, but when you want to revert to the original, you can simply use the command "Use RAW as original" while in EDIT mode, and can start editing from the original RAW file.

For example- I exported a raw file (a DNG) and the edited version as a JPEG. After reimporting them to another Library, the pair has been stacked and is showing the "J" badge.

The exported files:

The imported image:

Apple's Aperture could do this, but it has been expensive compared to the free Photos.

Apple did unfortunately not offer a successor for its professional photo application, when Aperture has been discontinued. The target audience for Photos are not the professional users or the ambitious amateurs.