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/experiment/ndt7/dial.go

@@ -0,0 +1,91 @@
+package ndt7
+
+import (
+	"context"
+	"crypto/tls"
+	"net/http"
+	"net/url"
+
+	"github.com/gorilla/websocket"
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/dialer"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/resolver"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/selfcensor"
+)
+
+type dialManager struct {
+	ndt7URL         string
+	logger          model.Logger
+	proxyURL        *url.URL
+	readBufferSize  int
+	tlsConfig       *tls.Config
+	userAgent       string
+	writeBufferSize int
+}
+
+func newDialManager(ndt7URL string, logger model.Logger, userAgent string) dialManager {
+	return dialManager{
+		ndt7URL:         ndt7URL,
+		logger:          logger,
+		readBufferSize:  paramMaxBufferSize,
+		userAgent:       userAgent,
+		writeBufferSize: paramMaxBufferSize,
+	}
+}
+
+func (mgr dialManager) dialWithTestName(ctx context.Context, testName string) (*websocket.Conn, error) {
+	var reso resolver.Resolver = resolver.SystemResolver{}
+	reso = resolver.LoggingResolver{Resolver: reso, Logger: mgr.logger}
+	var dlr dialer.Dialer = selfcensor.SystemDialer{}
+	dlr = dialer.TimeoutDialer{Dialer: dlr}
+	dlr = dialer.ErrorWrapperDialer{Dialer: dlr}
+	dlr = dialer.LoggingDialer{Dialer: dlr, Logger: mgr.logger}
+	dlr = dialer.DNSDialer{Dialer: dlr, Resolver: reso}
+	dlr = dialer.ProxyDialer{Dialer: dlr, ProxyURL: mgr.proxyURL}
+	dlr = dialer.ByteCounterDialer{Dialer: dlr}
+	dlr = dialer.ShapingDialer{Dialer: dlr}
+	dialer := websocket.Dialer{
+		NetDialContext:  dlr.DialContext,
+		ReadBufferSize:  mgr.readBufferSize,
+		TLSClientConfig: mgr.tlsConfig,
+		WriteBufferSize: mgr.writeBufferSize,
+	}
+	headers := http.Header{}
+	headers.Add("Sec-WebSocket-Protocol", "net.measurementlab.ndt.v7")
+	headers.Add("User-Agent", mgr.userAgent)
+	mgr.logrequest(mgr.ndt7URL, headers)
+	conn, _, err := dialer.DialContext(ctx, mgr.ndt7URL, headers)
+	mgr.logresponse(err)
+	return conn, err
+}
+
+func (mgr dialManager) logrequest(url string, headers http.Header) {
+	mgr.logger.Debugf("> GET %s", url)
+	for key, values := range headers {
+		for _, v := range values {
+			mgr.logger.Debugf("> %s: %s", key, v)
+		}
+	}
+	mgr.logger.Debug("> Connection: upgrade")
+	mgr.logger.Debug("> Upgrade: websocket")
+	mgr.logger.Debug(">")
+}
+
+func (mgr dialManager) logresponse(err error) {
+	if err != nil {
+		mgr.logger.Debugf("< %+v", err)
+		return
+	}
+	mgr.logger.Debug("< 101")
+	mgr.logger.Debug("< Connection: upgrade")
+	mgr.logger.Debug("< Upgrade: websocket")
+	mgr.logger.Debug("<")
+}
+
+func (mgr dialManager) dialDownload(ctx context.Context) (*websocket.Conn, error) {
+	return mgr.dialWithTestName(ctx, "download")
+}
+
+func (mgr dialManager) dialUpload(ctx context.Context) (*websocket.Conn, error) {
+	return mgr.dialWithTestName(ctx, "upload")
+}