fixes#22227
rationale:
- `3u - 4u` is supported why not`3u.toRational - 4u.toRational`
- all of rationals' api is on SomeInteger, looks like unsigned is
declared as supported
- math on unsigned rationals is meaningful and useful.
* make more standard libraries work with `nimPreviewSlimSystem`
* typo
* part two
* Delete specutils.nim
* fixes more tests
* more fixes
* fixes tests
* fixes three more tests
* add formatfloat import
* fix
* last