Change Details

Also `transform_view::iterator::base() const&`. Drive-by: stop calling `.base()` on test iterators in the test.

Also `transform_view::iterator::base() const&` should not be constrained. Drive-by: stop calling `.base()` on test iterators in the test.

Also `transform_view::iterator::base() const&` should not be constrained. Drive-by: stop calling `.base()` on test iterators in the test.