This diff changes the data format to prefer "udp" to "quic" everywhere we were previously using "quic".
Previously, the code inconsistently used "quic" for operations where we knew we were using "quic" and "udp" otherwise (e.g., for generic operations like ReadFrom).
While it would be more correct to say that a specific HTTP request used "quic" rather than "udp", using "udp" consistently allows one to see how distinct events such as ReadFrom and an handshake all refer to the same address, port, and protocol triple. Therefore, this change makes it easier to programmatically unpack a single measurement and create endpoint stats.
Before implementing this change, I discussed the problem with @hellais who mentioned that ooni/data is not currently using the "quic" string anywhere. I know that ooni/pipeline also doesn't rely on this string. The only users of this feature have been research-oriented experiments such as urlgetter, for which such a change would actually be acceptable.
See https://github.com/ooni/probe/issues/2238 and https://github.com/ooni/spec/pull/262.
Before finishing the ongoing refactoring and leaving whatever
is left of netx in tree, I would like to restructure it so that
we'll have an easy time next time we need to modify it.
Currently, every functionality lives into the `netx.go` file and
we have a support file called `httptransport.go`.
I would like to reorganize by topic, instead. This would allow
future me to more easily perform topic-specific changes.
While there, improve `netx`'s documentation and duplicate some of
this documentation inside `internal/README.md` to provide pointers
to previous documentation, historical context, and some help to
understand the logic architecture of network extensions (aka `netx`).
Part of https://github.com/ooni/probe-cli/pull/396
