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/resolver/integration_test.go

@@ -0,0 +1,111 @@
+package resolver_test
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"testing"
+
+	"github.com/apex/log"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/resolver"
+)
+
+func init() {
+	log.SetLevel(log.DebugLevel)
+}
+
+func testresolverquick(t *testing.T, reso resolver.Resolver) {
+	if testing.Short() {
+		t.Skip("skip test in short mode")
+	}
+	reso = resolver.LoggingResolver{Logger: log.Log, Resolver: reso}
+	addrs, err := reso.LookupHost(context.Background(), "dns.google.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if addrs == nil {
+		t.Fatal("expected non-nil addrs here")
+	}
+	var foundquad8 bool
+	for _, addr := range addrs {
+		// See https://github.com/ooni/probe-cli/v3/internal/engine/pull/954/checks?check_run_id=1182269025
+		if addr == "8.8.8.8" || addr == "2001:4860:4860::8888" {
+			foundquad8 = true
+		}
+	}
+	if !foundquad8 {
+		t.Fatalf("did not find 8.8.8.8 in ouput; output=%+v", addrs)
+	}
+}
+
+// Ensuring we can handle Internationalized Domain Names (IDNs) without issues
+func testresolverquickidna(t *testing.T, reso resolver.Resolver) {
+	if testing.Short() {
+		t.Skip("skip test in short mode")
+	}
+	reso = resolver.IDNAResolver{
+		resolver.LoggingResolver{Logger: log.Log, Resolver: reso},
+	}
+	addrs, err := reso.LookupHost(context.Background(), "яндекс.рф")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if addrs == nil {
+		t.Fatal("expected non-nil addrs here")
+	}
+}
+
+func TestNewResolverSystem(t *testing.T) {
+	reso := resolver.SystemResolver{}
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverUDPAddress(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverUDP(new(net.Dialer), "8.8.8.8:53"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverUDPDomain(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverUDP(new(net.Dialer), "dns.google.com:53"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverTCPAddress(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverTCP(new(net.Dialer).DialContext, "8.8.8.8:53"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverTCPDomain(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverTCP(new(net.Dialer).DialContext, "dns.google.com:53"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverDoTAddress(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverTLS(resolver.DialTLSContext, "8.8.8.8:853"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverDoTDomain(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverTLS(resolver.DialTLSContext, "dns.google.com:853"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}
+
+func TestNewResolverDoH(t *testing.T) {
+	reso := resolver.NewSerialResolver(
+		resolver.NewDNSOverHTTPS(http.DefaultClient, "https://cloudflare-dns.com/dns-query"))
+	testresolverquick(t, reso)
+	testresolverquickidna(t, reso)
+}