feat(oohelperd): log messages at info level (#896)

We're using a request-specific logger where we also print the ID
of the request. This design helps to observe logs produced by
concurrent requests.

Part of https://github.com/ooni/probe/issues/2183

While there, fix https://github.com/ooni/probe/issues/2241

internal/cmd/oohelperd/logging_test.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
+)
+
+func TestIndexLogger(t *testing.T) {
+	t.Run("Debug", func(t *testing.T) {
+		expected := "<0>antani"
+		base := &mocks.Logger{
+			MockDebug: func(message string) {
+				if message != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Debug("antani")
+	})
+
+	t.Run("Info", func(t *testing.T) {
+		expected := "<0>antani"
+		base := &mocks.Logger{
+			MockInfo: func(message string) {
+				if message != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Info("antani")
+	})
+
+	t.Run("Warn", func(t *testing.T) {
+		expected := "<0>antani"
+		base := &mocks.Logger{
+			MockWarn: func(message string) {
+				if message != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Warn("antani")
+	})
+
+	t.Run("Debugf", func(t *testing.T) {
+		expected := "<0>antani%d"
+		base := &mocks.Logger{
+			MockDebugf: func(format string, v ...any) {
+				if format != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Debugf("antani%d", 11)
+	})
+
+	t.Run("Infof", func(t *testing.T) {
+		expected := "<0>antani%d"
+		base := &mocks.Logger{
+			MockInfof: func(format string, v ...any) {
+				if format != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Infof("antani%d", 11)
+	})
+
+	t.Run("Warnf", func(t *testing.T) {
+		expected := "<0>antani%d"
+		base := &mocks.Logger{
+			MockWarnf: func(format string, v ...any) {
+				if format != expected {
+					t.Fatal("unexpected message")
+				}
+			},
+		}
+		logger := &indexLogger{
+			indexstr: "<0>",
+			logger:   base,
+		}
+		logger.Warnf("antani%d", 11)
+	})
+}