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/dialer/logging.go

@@ -0,0 +1,56 @@
+package dialer
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/internal/tlsx"
+)
+
+// Logger is the logger assumed by this package
+type Logger interface {
+	Debugf(format string, v ...interface{})
+	Debug(message string)
+}
+
+// LoggingDialer is a Dialer with logging
+type LoggingDialer struct {
+	Dialer
+	Logger Logger
+}
+
+// DialContext implements Dialer.DialContext
+func (d LoggingDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	d.Logger.Debugf("dial %s/%s...", address, network)
+	start := time.Now()
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	stop := time.Now()
+	d.Logger.Debugf("dial %s/%s... %+v in %s", address, network, err, stop.Sub(start))
+	return conn, err
+}
+
+// LoggingTLSHandshaker is a TLSHandshaker with logging
+type LoggingTLSHandshaker struct {
+	TLSHandshaker
+	Logger Logger
+}
+
+// Handshake implements Handshaker.Handshake
+func (h LoggingTLSHandshaker) Handshake(
+	ctx context.Context, conn net.Conn, config *tls.Config,
+) (net.Conn, tls.ConnectionState, error) {
+	h.Logger.Debugf("tls {sni=%s next=%+v}...", config.ServerName, config.NextProtos)
+	start := time.Now()
+	tlsconn, state, err := h.TLSHandshaker.Handshake(ctx, conn, config)
+	stop := time.Now()
+	h.Logger.Debugf(
+		"tls {sni=%s next=%+v}... %+v in %s {next=%s cipher=%s v=%s}", config.ServerName,
+		config.NextProtos, err, stop.Sub(start), state.NegotiatedProtocol,
+		tlsx.CipherSuiteString(state.CipherSuite), tlsx.VersionString(state.Version))
+	return tlsconn, state, err
+}
+
+var _ Dialer = LoggingDialer{}
+var _ TLSHandshaker = LoggingTLSHandshaker{}