race: Use Self ubiquitously.

[briansmith]

Avoid repeating type parameters and otherwise make it easier to see where a function is a constructor.

[matklad]

I personally prefer not to use self, as Self requires an extra mental dereference to figure out what the type actually is, but, at this point, using Self is clearly considered much more idiomatic in Rust, and you've been working on this code lately so its for you to call the shots!