make quantify work with no_unit

[andrewgsavage]

• [x] Closes #46 #119
• [x] Executed pre-commit run --all-files with no errors
• [x] The change is fully covered by automated unit tests
• [x] Documented in docs/ as appropriate
• [x] Added an entry to the CHANGES file

[andrewgsavage]

This is ready for merging

[andrewgsavage]

bors r+

[bors[bot]]

Build failed:

• ci

[andrewgsavage]

bors r+

[bors[bot]]

Build succeeded:

• ci
• lint