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/oonimkall/tasks/runner_internal_test.go

@@ -0,0 +1,72 @@
+package tasks
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"testing"
+
+	engine "github.com/ooni/probe-cli/v3/internal/engine"
+)
+
+func TestMeasurementSubmissionEventName(t *testing.T) {
+	if measurementSubmissionEventName(nil) != statusMeasurementSubmission {
+		t.Fatal("unexpected submission event name")
+	}
+	if measurementSubmissionEventName(errors.New("mocked error")) != failureMeasurementSubmission {
+		t.Fatal("unexpected submission event name")
+	}
+}
+
+func TestMeasurementSubmissionFailure(t *testing.T) {
+	if measurementSubmissionFailure(nil) != "" {
+		t.Fatal("unexpected submission failure")
+	}
+	if measurementSubmissionFailure(errors.New("mocked error")) != "mocked error" {
+		t.Fatal("unexpected submission failure")
+	}
+}
+
+func TestRunnerMaybeLookupLocationFailure(t *testing.T) {
+	out := make(chan *Event)
+	settings := &Settings{
+		AssetsDir: "../../testdata/oonimkall/assets",
+		Name:      "Example",
+		Options: SettingsOptions{
+			SoftwareName:    "oonimkall-test",
+			SoftwareVersion: "0.1.0",
+		},
+		StateDir: "../../testdata/oonimkall/state",
+		Version:  1,
+	}
+	seench := make(chan int64)
+	go func() {
+		var seen int64
+		for ev := range out {
+			switch ev.Key {
+			case "failure.ip_lookup", "failure.asn_lookup",
+				"failure.cc_lookup", "failure.resolver_lookup":
+				seen++
+			case "status.progress":
+				evv := ev.Value.(EventStatusProgress)
+				if evv.Percentage >= 0.2 {
+					panic(fmt.Sprintf("too much progress: %+v", ev))
+				}
+			case "status.queued", "status.started", "status.end":
+			default:
+				panic(fmt.Sprintf("unexpected key: %s", ev.Key))
+			}
+		}
+		seench <- seen
+	}()
+	expected := errors.New("mocked error")
+	r := NewRunner(settings, out)
+	r.maybeLookupLocation = func(*engine.Session) error {
+		return expected
+	}
+	r.Run(context.Background())
+	close(out)
+	if n := <-seench; n != 4 {
+		t.Fatal("unexpected number of events")
+	}
+}