Parsing Url is one of the most expensive things that async-h1 does

In most cases, we parse a url from host and path and then later on only use the path for routing. Holding two &str's on Request and only generating a url if/when it's required would provide performance gains.

Start by tracing how Request stores and parses the host and path, then follow how routing consumes those values. Compare the current eager URL parsing with the proposed lazy URL generation; done means routing can use separate host and path references while a URL is generated only when required, without changing request behavior.

Written by the indexing model from the issue text.