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/saver.go

@@ -0,0 +1,125 @@
+package dialer
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/internal/tlsx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
+)
+
+// SaverDialer saves events occurring during the dial
+type SaverDialer struct {
+	Dialer
+	Saver *trace.Saver
+}
+
+// DialContext implements Dialer.DialContext
+func (d SaverDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	start := time.Now()
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	stop := time.Now()
+	d.Saver.Write(trace.Event{
+		Address:  address,
+		Duration: stop.Sub(start),
+		Err:      err,
+		Name:     errorx.ConnectOperation,
+		Proto:    network,
+		Time:     stop,
+	})
+	return conn, err
+}
+
+// SaverTLSHandshaker saves events occurring during the handshake
+type SaverTLSHandshaker struct {
+	TLSHandshaker
+	Saver *trace.Saver
+}
+
+// Handshake implements TLSHandshaker.Handshake
+func (h SaverTLSHandshaker) Handshake(
+	ctx context.Context, conn net.Conn, config *tls.Config,
+) (net.Conn, tls.ConnectionState, error) {
+	start := time.Now()
+	h.Saver.Write(trace.Event{
+		Name:          "tls_handshake_start",
+		NoTLSVerify:   config.InsecureSkipVerify,
+		TLSNextProtos: config.NextProtos,
+		TLSServerName: config.ServerName,
+		Time:          start,
+	})
+	tlsconn, state, err := h.TLSHandshaker.Handshake(ctx, conn, config)
+	stop := time.Now()
+	h.Saver.Write(trace.Event{
+		Duration:           stop.Sub(start),
+		Err:                err,
+		Name:               "tls_handshake_done",
+		NoTLSVerify:        config.InsecureSkipVerify,
+		TLSCipherSuite:     tlsx.CipherSuiteString(state.CipherSuite),
+		TLSNegotiatedProto: state.NegotiatedProtocol,
+		TLSNextProtos:      config.NextProtos,
+		TLSPeerCerts:       trace.PeerCerts(state, err),
+		TLSServerName:      config.ServerName,
+		TLSVersion:         tlsx.VersionString(state.Version),
+		Time:               stop,
+	})
+	return tlsconn, state, err
+}
+
+// SaverConnDialer wraps the returned connection such that we
+// collect all the read/write events that occur.
+type SaverConnDialer struct {
+	Dialer
+	Saver *trace.Saver
+}
+
+// DialContext implements Dialer.DialContext
+func (d SaverConnDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	if err != nil {
+		return nil, err
+	}
+	return saverConn{saver: d.Saver, Conn: conn}, nil
+}
+
+type saverConn struct {
+	net.Conn
+	saver *trace.Saver
+}
+
+func (c saverConn) Read(p []byte) (int, error) {
+	start := time.Now()
+	count, err := c.Conn.Read(p)
+	stop := time.Now()
+	c.saver.Write(trace.Event{
+		Data:     p[:count],
+		Duration: stop.Sub(start),
+		Err:      err,
+		NumBytes: count,
+		Name:     errorx.ReadOperation,
+		Time:     stop,
+	})
+	return count, err
+}
+
+func (c saverConn) Write(p []byte) (int, error) {
+	start := time.Now()
+	count, err := c.Conn.Write(p)
+	stop := time.Now()
+	c.saver.Write(trace.Event{
+		Data:     p[:count],
+		Duration: stop.Sub(start),
+		Err:      err,
+		NumBytes: count,
+		Name:     errorx.WriteOperation,
+		Time:     stop,
+	})
+	return count, err
+}
+
+var _ Dialer = SaverDialer{}
+var _ TLSHandshaker = SaverTLSHandshaker{}
+var _ net.Conn = saverConn{}