walk: move NewListRHelper into list.Helper to avoid circular dependency

It turns out that the list helpers were at the wrong level and needed
to be pushed down into the fs/list for future work.

fs/list/helpers_test.go

@@ -0,0 +1,90 @@
+package list
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fstest/mockobject"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Mock callback to collect the entries
+func mockCallback(entries fs.DirEntries) error {
+	// Do nothing or log for testing purposes
+	return nil
+}
+
+func TestNewListRHelper(t *testing.T) {
+	callback := mockCallback
+	helper := NewHelper(callback)
+
+	assert.NotNil(t, helper)
+	assert.Equal(t, fmt.Sprintf("%p", callback), fmt.Sprintf("%p", helper.callback))
+	assert.Empty(t, helper.entries)
+}
+
+func TestListRHelperAdd(t *testing.T) {
+	callbackInvoked := false
+	callback := func(entries fs.DirEntries) error {
+		callbackInvoked = true
+		return nil
+	}
+
+	helper := NewHelper(callback)
+	entry := mockobject.Object("A")
+	require.NoError(t, helper.Add(entry))
+
+	assert.Len(t, helper.entries, 1)
+	assert.False(t, callbackInvoked, "Callback should not be invoked before reaching 100 entries")
+
+	// Check adding a nil entry doesn't change anything
+	require.NoError(t, helper.Add(nil))
+	assert.Len(t, helper.entries, 1)
+	assert.False(t, callbackInvoked, "Callback should not be invoked before reaching 100 entries")
+}
+
+func TestListRHelperSend(t *testing.T) {
+	entry := mockobject.Object("A")
+	callbackInvoked := false
+	callback := func(entries fs.DirEntries) error {
+		callbackInvoked = true
+		assert.Equal(t, 100, len(entries))
+		for _, obj := range entries {
+			assert.Equal(t, entry, obj)
+		}
+		return nil
+	}
+
+	helper := NewHelper(callback)
+
+	// Add 100 entries to force the callback to be invoked
+	for i := 0; i < 100; i++ {
+		require.NoError(t, helper.Add(entry))
+	}
+
+	assert.Len(t, helper.entries, 0)
+	assert.True(t, callbackInvoked, "Callback should be invoked after 100 entries")
+}
+
+func TestListRHelperFlush(t *testing.T) {
+	entry := mockobject.Object("A")
+	callbackInvoked := false
+	callback := func(entries fs.DirEntries) error {
+		callbackInvoked = true
+		assert.Equal(t, 1, len(entries))
+		for _, obj := range entries {
+			assert.Equal(t, entry, obj)
+		}
+		return nil
+	}
+
+	helper := NewHelper(callback)
+	require.NoError(t, helper.Add(entry))
+	assert.False(t, callbackInvoked, "Callback should not have been invoked yet")
+	require.NoError(t, helper.Flush())
+
+	assert.True(t, callbackInvoked, "Callback should be invoked on flush")
+	assert.Len(t, helper.entries, 0, "Entries should be cleared after flush")
+}