Shouldn't the formatter consider this whitespace using the new Unicode support?

Yup, it's good idea if formatter could detect this because it is difficult for human to notice in editors and browsers.
Although intended use of c2a0 exists like following, it doesn't disturb formatter because it must be only in string literals not program codes.
https://github.com/crystal-lang/crystal/blob/master/spec/std/html_spec.cr#L24-L25

Thank you!