Networking (HTTP, filesystem, Data URIs) for Blitz
Provides implementations of [blitz_traits::net::NetProvider], which loads
the resources a document needs, and of
[blitz_traits::platform::FetchProvider], which serves a guest's fetch().
Both run on the one client. Provider holds a single reqwest::Client,
built once with HTTP/2, the cookie jar, the compression codecs and the
cacache disk cache, plus one per-host semaphore enforcing the browser's cap
of six concurrent requests per origin. A guest's fetch therefore shares
the connection pool, the cookies and the cache with the page's own loads,
and counts against the same concurrency budget, which is what a browser
does. A second client would have given a guest its own cookie jar and its
own six connections per host.