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/submitter_test.go

@@ -0,0 +1,88 @@
+package engine
+
+import (
+	"context"
+	"errors"
+	"sync/atomic"
+	"testing"
+
+	"github.com/apex/log"
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+)
+
+func TestSubmitterNotEnabled(t *testing.T) {
+	ctx := context.Background()
+	submitter, err := NewSubmitter(ctx, SubmitterConfig{
+		Enabled: false,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := submitter.(stubSubmitter); !ok {
+		t.Fatal("we did not get a stubSubmitter instance")
+	}
+	m := new(model.Measurement)
+	if err := submitter.Submit(ctx, m); err != nil {
+		t.Fatal(err)
+	}
+}
+
+type FakeSubmitter struct {
+	Calls uint32
+	Error error
+}
+
+func (fs *FakeSubmitter) Submit(ctx context.Context, m *model.Measurement) error {
+	atomic.AddUint32(&fs.Calls, 1)
+	return fs.Error
+}
+
+var _ Submitter = &FakeSubmitter{}
+
+type FakeSubmitterSession struct {
+	Error     error
+	Submitter Submitter
+}
+
+func (fse FakeSubmitterSession) NewSubmitter(ctx context.Context) (Submitter, error) {
+	return fse.Submitter, fse.Error
+}
+
+var _ SubmitterSession = FakeSubmitterSession{}
+
+func TestNewSubmitterFails(t *testing.T) {
+	expected := errors.New("mocked error")
+	ctx := context.Background()
+	submitter, err := NewSubmitter(ctx, SubmitterConfig{
+		Enabled: true,
+		Session: FakeSubmitterSession{Error: expected},
+	})
+	if !errors.Is(err, expected) {
+		t.Fatalf("not the error we expected: %+v", err)
+	}
+	if submitter != nil {
+		t.Fatal("expected nil submitter here")
+	}
+}
+
+func TestNewSubmitterWithFailedSubmission(t *testing.T) {
+	expected := errors.New("mocked error")
+	ctx := context.Background()
+	fakeSubmitter := &FakeSubmitter{Error: expected}
+	submitter, err := NewSubmitter(ctx, SubmitterConfig{
+		Enabled: true,
+		Logger:  log.Log,
+		Session: FakeSubmitterSession{Submitter: fakeSubmitter},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m := new(model.Measurement)
+	err = submitter.Submit(context.Background(), m)
+	if !errors.Is(err, expected) {
+		t.Fatalf("not the error we expected: %+v", err)
+	}
+	if fakeSubmitter.Calls != 1 {
+		t.Fatal("unexpected number of calls")
+	}
+}