* 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.
## Checklist
- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/1885
- [x] related ooni/spec pull request: N/A
Location of the issue tracker: https://github.com/ooni/probe
## Description
This PR contains a set of changes to move important interfaces and data types into the `./internal/model` package.
The criteria for including an interface or data type in here is roughly that the type should be important and used by several packages. We are especially interested to move more interfaces here to increase modularity.
An additional side effect is that, by reading this package, one should be able to understand more quickly how different parts of the codebase interact with each other.
This is what I want to move in `internal/model`:
- [x] most important interfaces from `internal/netxlite`
- [x] everything that was previously part of `internal/engine/model`
- [x] mocks from `internal/netxlite/mocks` should also be moved in here as a subpackage
