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/emitter.go

@@ -0,0 +1,103 @@
+package dialer
+
+import (
+	"context"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/dialid"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
+	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/transactionid"
+)
+
+// EmitterDialer is a Dialer that emits events
+type EmitterDialer struct {
+	Dialer
+}
+
+// DialContext implements Dialer.DialContext
+func (d EmitterDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	start := time.Now()
+	conn, err := d.Dialer.DialContext(ctx, network, address)
+	stop := time.Now()
+	root := modelx.ContextMeasurementRootOrDefault(ctx)
+	root.Handler.OnMeasurement(modelx.Measurement{
+		Connect: &modelx.ConnectEvent{
+			ConnID:                 safeConnID(network, conn),
+			DialID:                 dialid.ContextDialID(ctx),
+			DurationSinceBeginning: stop.Sub(root.Beginning),
+			Error:                  err,
+			Network:                network,
+			RemoteAddress:          address,
+			SyscallDuration:        stop.Sub(start),
+			TransactionID:          transactionid.ContextTransactionID(ctx),
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	return EmitterConn{
+		Conn:      conn,
+		Beginning: root.Beginning,
+		Handler:   root.Handler,
+		ID:        safeConnID(network, conn),
+	}, nil
+}
+
+// EmitterConn is a net.Conn used to emit events
+type EmitterConn struct {
+	net.Conn
+	Beginning time.Time
+	Handler   modelx.Handler
+	ID        int64
+}
+
+// Read implements net.Conn.Read
+func (c EmitterConn) Read(b []byte) (n int, err error) {
+	start := time.Now()
+	n, err = c.Conn.Read(b)
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Read: &modelx.ReadEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			NumBytes:               int64(n),
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}
+
+// Write implements net.Conn.Write
+func (c EmitterConn) Write(b []byte) (n int, err error) {
+	start := time.Now()
+	n, err = c.Conn.Write(b)
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Write: &modelx.WriteEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			NumBytes:               int64(n),
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}
+
+// Close implements net.Conn.Close
+func (c EmitterConn) Close() (err error) {
+	start := time.Now()
+	err = c.Conn.Close()
+	stop := time.Now()
+	c.Handler.OnMeasurement(modelx.Measurement{
+		Close: &modelx.CloseEvent{
+			ConnID:                 c.ID,
+			DurationSinceBeginning: stop.Sub(c.Beginning),
+			Error:                  err,
+			SyscallDuration:        stop.Sub(start),
+		},
+	})
+	return
+}