This work aims to make Linux builds faster to make https://github.com/ooni/probe/issues/2249 more convenient. Since those builds runs inside Docker, the problem to solve here is to save/restore the Go caches notwithstanding Docker. Because Docker runs as root, we need to modify the build a bit to run as a normal user. Otherwise, we will not be able to save the Go cache using actions/cache@v3. (Other approaches such as using `sudo` are possible but running the build as an unprivileged user actually looks cleaner, so I chose to do that.) While there, add a `.editorconfig`.
* upgrade to our go.mod enabled of psiphon-tunnel-core such that
we're now using v2.0.24 of the tunnel-core;
* upgrade to the latest lucas-clemente/quic-go release;
* upgrade to the latest ooni/oohttp release (which is based on go1.19
but the diff seems good enough to continue using go1.18.x as well);
* upgrade to the latest ooni/oocrypto release (for which we can make the
same remarks regarding using go1.18.x);
* deal with changes in lucas-clemente/quic-go API as well as changes
in what a go1.19 *tls.Conn compatible type should look like.
Unfortunately, we cannot switch to go1.19 because psiphon forks quic-go
and their fork's still not building using such a version of go.
Part of ooni/probe#2211.
