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/probeservices/tor_test.go

@@ -0,0 +1,82 @@
+package probeservices_test
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/engine/probeservices/testorchestra"
+)
+
+func TestFetchTorTargets(t *testing.T) {
+	clnt := newclient()
+	if err := clnt.MaybeRegister(context.Background(), testorchestra.MetadataFixture()); err != nil {
+		t.Fatal(err)
+	}
+	if err := clnt.MaybeLogin(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	data, err := clnt.FetchTorTargets(context.Background(), "ZZ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if data == nil || len(data) <= 0 {
+		t.Fatal("invalid data")
+	}
+}
+
+func TestFetchTorTargetsNotRegistered(t *testing.T) {
+	clnt := newclient()
+	state := probeservices.State{
+		// Explicitly empty so the test is more clear
+	}
+	if err := clnt.StateFile.Set(state); err != nil {
+		t.Fatal(err)
+	}
+	data, err := clnt.FetchTorTargets(context.Background(), "ZZ")
+	if err == nil {
+		t.Fatal("expected an error here")
+	}
+	if data != nil {
+		t.Fatal("expected nil data here")
+	}
+}
+
+type FetchTorTargetsHTTPTransport struct {
+	Response *http.Response
+}
+
+func (clnt *FetchTorTargetsHTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	resp, err := http.DefaultTransport.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+	if req.URL.Path == "/api/v1/test-list/tor-targets" {
+		clnt.Response = resp
+	}
+	return resp, err
+}
+
+func TestFetchTorTargetsSetsQueryString(t *testing.T) {
+	clnt := newclient()
+	txp := new(FetchTorTargetsHTTPTransport)
+	clnt.HTTPClient.Transport = txp
+	if err := clnt.MaybeRegister(context.Background(), testorchestra.MetadataFixture()); err != nil {
+		t.Fatal(err)
+	}
+	if err := clnt.MaybeLogin(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	data, err := clnt.FetchTorTargets(context.Background(), "ZZ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if data == nil || len(data) <= 0 {
+		t.Fatal("invalid data")
+	}
+	requestURL := txp.Response.Request.URL
+	if requestURL.Query().Get("country_code") != "ZZ" {
+		t.Fatal("invalid country code")
+	}
+}