LGTM overall. Please don't forget the conformance tests!
Wasn't this already in the subrange patch?
Can you test with some standard library types, for example std:;string, std::vector, std::string_view, and std::span.
Adds range conformance tests.
This also needs a subsumption test. Once that's in place, I'll review it and likely LGTM it!
Add subsumption test.
LGTM! Make sure it passes CI before committing.