actix_router: Leaking strings causes LeakSanitizer noise

[bugadani]

ResourceDef leaks strings on purpose, which makes LeakSanitizer output rather messy, since the strings aren't explicitly free'd. I understand why this is (and why it's not a problem for execution), but this makes using LeakSanitizer rather ... unwieldy.

I'm also unsure what could be done here - dropping strings when the ResourceDef is dropped isn't exactly safe, and using Rc<String> instead would (I guess) be a perf hit.