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/experiment_test.go

@@ -0,0 +1,75 @@
+package engine
+
+import (
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/geolocate"
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+)
+
+func TestExperimentHonoursSharingDefaults(t *testing.T) {
+	measure := func(info *geolocate.Results) *model.Measurement {
+		sess := &Session{location: info}
+		builder, err := sess.NewExperimentBuilder("example")
+		if err != nil {
+			t.Fatal(err)
+		}
+		exp := builder.NewExperiment()
+		return exp.newMeasurement("")
+	}
+	type spec struct {
+		name         string
+		locationInfo *geolocate.Results
+		expect       func(*model.Measurement) bool
+	}
+	allspecs := []spec{{
+		name:         "probeIP",
+		locationInfo: &geolocate.Results{ProbeIP: "8.8.8.8"},
+		expect: func(m *model.Measurement) bool {
+			return m.ProbeIP == geolocate.DefaultProbeIP
+		},
+	}, {
+		name:         "probeASN",
+		locationInfo: &geolocate.Results{ASN: 30722},
+		expect: func(m *model.Measurement) bool {
+			return m.ProbeASN == "AS30722"
+		},
+	}, {
+		name:         "probeCC",
+		locationInfo: &geolocate.Results{CountryCode: "IT"},
+		expect: func(m *model.Measurement) bool {
+			return m.ProbeCC == "IT"
+		},
+	}, {
+		name:         "probeNetworkName",
+		locationInfo: &geolocate.Results{NetworkName: "Vodafone Italia"},
+		expect: func(m *model.Measurement) bool {
+			return m.ProbeNetworkName == "Vodafone Italia"
+		},
+	}, {
+		name:         "resolverIP",
+		locationInfo: &geolocate.Results{ResolverIP: "9.9.9.9"},
+		expect: func(m *model.Measurement) bool {
+			return m.ResolverIP == "9.9.9.9"
+		},
+	}, {
+		name:         "resolverASN",
+		locationInfo: &geolocate.Results{ResolverASN: 44},
+		expect: func(m *model.Measurement) bool {
+			return m.ResolverASN == "AS44"
+		},
+	}, {
+		name:         "resolverNetworkName",
+		locationInfo: &geolocate.Results{ResolverNetworkName: "Google LLC"},
+		expect: func(m *model.Measurement) bool {
+			return m.ResolverNetworkName == "Google LLC"
+		},
+	}}
+	for _, spec := range allspecs {
+		t.Run(spec.name, func(t *testing.T) {
+			if !spec.expect(measure(spec.locationInfo)) {
+				t.Fatal("expectation failed")
+			}
+		})
+	}
+}