chore: merge probe-engine into probe-cli (#201)

This is how I did it:

1. `git clone https://github.com/ooni/probe-engine internal/engine`

2. ```
(cd internal/engine && git describe --tags)
v0.23.0
```

3. `nvim go.mod` (merging `go.mod` with `internal/engine/go.mod`

4. `rm -rf internal/.git internal/engine/go.{mod,sum}`

5. `git add internal/engine`

6. `find . -type f -name \*.go -exec sed -i 's@/ooni/probe-engine@/ooni/probe-cli/v3/internal/engine@g' {} \;`

7. `go build ./...` (passes)

8. `go test -race ./...` (temporary failure on RiseupVPN)

9. `go mod tidy`

10. this commit message

Once this piece of work is done, we can build a new version of `ooniprobe` that
is using `internal/engine` directly. We need to do more work to ensure all the
other functionality in `probe-engine` (e.g. making mobile packages) are still WAI.

Part of https://github.com/ooni/probe/issues/1335

internal/engine/netx/quicdialer/errorwrapper_test.go

@@ -0,0 +1,61 @@
+package quicdialer_test
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"io"
+	"testing"
+
+	"github.com/lucas-clemente/quic-go"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/dialid"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/quicdialer"
+)
+
+func TestErrorWrapperFailure(t *testing.T) {
+	ctx := dialid.WithDialID(context.Background())
+	d := quicdialer.ErrorWrapperDialer{
+		Dialer: MockDialer{Sess: nil, Err: io.EOF}}
+	sess, err := d.DialContext(
+		ctx, "udp", "www.google.com:443", &tls.Config{}, &quic.Config{})
+	if sess != nil {
+		t.Fatal("expected a nil sess here")
+	}
+	errorWrapperCheckErr(t, err, errorx.QUICHandshakeOperation)
+}
+
+func errorWrapperCheckErr(t *testing.T, err error, op string) {
+	if !errors.Is(err, io.EOF) {
+		t.Fatal("expected another error here")
+	}
+	var errWrapper *errorx.ErrWrapper
+	if !errors.As(err, &errWrapper) {
+		t.Fatal("cannot cast to ErrWrapper")
+	}
+	if errWrapper.DialID == 0 {
+		t.Fatal("unexpected DialID")
+	}
+	if errWrapper.Operation != op {
+		t.Fatal("unexpected Operation")
+	}
+	if errWrapper.Failure != errorx.FailureEOFError {
+		t.Fatal("unexpected failure")
+	}
+}
+
+func TestErrorWrapperSuccess(t *testing.T) {
+	ctx := dialid.WithDialID(context.Background())
+	tlsConf := &tls.Config{
+		NextProtos: []string{"h3-29"},
+		ServerName: "www.google.com",
+	}
+	d := quicdialer.ErrorWrapperDialer{Dialer: quicdialer.SystemDialer{}}
+	sess, err := d.DialContext(ctx, "udp", "216.58.212.164:443", tlsConf, &quic.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sess == nil {
+		t.Fatal("expected non-nil sess here")
+	}
+}