feat: tlsping and tcpping using step-by-step (#815)

## Checklist

- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/2158
- [x] if you changed anything related how experiments work and you need to reflect these changes in the ooni/spec repository, please link to the related ooni/spec pull request: https://github.com/ooni/spec/pull/250

## Description

This diff refactors the codebase to reimplement tlsping and tcpping
to use the step-by-step measurements style.

See docs/design/dd-003-step-by-step.md for more information on the
step-by-step measurement style.

internal/model/mocks/trace.go

@@ -0,0 +1,45 @@
+package mocks
+
+//
+// Mocks for model.Trace
+//
+
+import (
+	"crypto/tls"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
+)
+
+// Trace allows mocking model.Trace.
+type Trace struct {
+	MockTimeNow func() time.Time
+
+	MockOnConnectDone func(
+		started time.Time, network, domain, remoteAddr string, err error, finished time.Time)
+
+	MockOnTLSHandshakeStart func(now time.Time, remoteAddr string, config *tls.Config)
+
+	MockOnTLSHandshakeDone func(started time.Time, remoteAddr string, config *tls.Config,
+		state tls.ConnectionState, err error, finished time.Time)
+}
+
+var _ model.Trace = &Trace{}
+
+func (t *Trace) TimeNow() time.Time {
+	return t.MockTimeNow()
+}
+
+func (t *Trace) OnConnectDone(
+	started time.Time, network, domain, remoteAddr string, err error, finished time.Time) {
+	t.MockOnConnectDone(started, network, domain, remoteAddr, err, finished)
+}
+
+func (t *Trace) OnTLSHandshakeStart(now time.Time, remoteAddr string, config *tls.Config) {
+	t.MockOnTLSHandshakeStart(now, remoteAddr, config)
+}
+
+func (t *Trace) OnTLSHandshakeDone(started time.Time, remoteAddr string, config *tls.Config,
+	state tls.ConnectionState, err error, finished time.Time) {
+	t.MockOnTLSHandshakeDone(started, remoteAddr, config, state, err, finished)
+}

internal/model/mocks/trace_test.go

@@ -0,0 +1,74 @@
+package mocks
+
+import (
+	"crypto/tls"
+	"testing"
+	"time"
+)
+
+func TestTrace(t *testing.T) {
+	t.Run("TimeNow", func(t *testing.T) {
+		now := time.Now()
+		tx := &Trace{
+			MockTimeNow: func() time.Time {
+				return now
+			},
+		}
+		if !tx.TimeNow().Equal(now) {
+			t.Fatal("not working as intended")
+		}
+	})
+
+	t.Run("OnConnectDone", func(t *testing.T) {
+		var called bool
+		tx := &Trace{
+			MockOnConnectDone: func(started time.Time, network, domain, remoteAddr string, err error, finished time.Time) {
+				called = true
+			},
+		}
+		tx.OnConnectDone(
+			time.Now(),
+			"tcp",
+			"dns.google",
+			"8.8.8.8:443",
+			nil,
+			time.Now(),
+		)
+		if !called {
+			t.Fatal("not called")
+		}
+	})
+
+	t.Run("OnTLSHandshakeStart", func(t *testing.T) {
+		var called bool
+		tx := &Trace{
+			MockOnTLSHandshakeStart: func(now time.Time, remoteAddr string, config *tls.Config) {
+				called = true
+			},
+		}
+		tx.OnTLSHandshakeStart(time.Now(), "8.8.8.8:443", &tls.Config{})
+		if !called {
+			t.Fatal("not called")
+		}
+	})
+
+	t.Run("OnTLSHandshakeDone", func(t *testing.T) {
+		var called bool
+		tx := &Trace{
+			MockOnTLSHandshakeDone: func(started time.Time, remoteAddr string, config *tls.Config, state tls.ConnectionState, err error, finished time.Time) {
+				called = true
+			},
+		}
+		tx.OnTLSHandshakeDone(
+			time.Now(),
+			"8.8.8.8:443",
+			&tls.Config{},
+			tls.ConnectionState{},
+			nil,
+			time.Now(),
+		)
+		if !called {
+			t.Fatal("not called")
+		}
+	})
+}