puffin-client: simplify use of http-cache-semantics (#1197)
The `http-cache-semantics` crate is polymorphic on the types of requests
and responses it accepts. We had previously been explicitly converting
between `http` and `reqwest` types, but this isn't necessary. We can
provide impls of the traits in `http-cache-semantics` for `reqwest`'s
types (via a wrapper). This saves us from the awkward request/response
type conversions.
While this does clone the request, this is:
1. Not new. We were previously cloning the request to do the conversion.
2. An artifact (I believe) of http-cache-semantics API. (It kind of
seems like an API bug to me?)
There is also a little bit of messiness around inter-operating between
http::uri::Uri and url::Url. But overall shouldn't be a big deal.
