Add prefetch collection for groups (#4906)

<!-- PR description-->

Minor refactor before introducing `lazyFetchCollection` for groups. We'll utilize `lazyFetchCollection` for group mailboxes and will continue to use `prefetchCollection` for channels.


---

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [x] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* https://github.com/alcionai/corso/issues/4862

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/m365/collection/groups/backup.go

@@ -4,7 +4,6 @@ import (
 	"context"
 
 	"github.com/alcionai/clues"
-	"golang.org/x/exp/maps"
 
 	"github.com/alcionai/corso/src/internal/common/pii"
 	"github.com/alcionai/corso/src/internal/common/ptr"
@@ -174,10 +173,9 @@ func populateCollections[C graph.GetIDer, I groupsItemer](
 			continue
 		}
 
-		added := str.SliceToMap(maps.Keys(addAndRem.Added))
 		removed := str.SliceToMap(addAndRem.Removed)
 
-		cl.Add(count.ItemsAdded, int64(len(added)))
+		cl.Add(count.ItemsAdded, int64(len(addAndRem.Added)))
 		cl.Add(count.ItemsRemoved, int64(len(removed)))
 
 		if len(addAndRem.DU.URL) > 0 {
@@ -198,7 +196,7 @@ func populateCollections[C graph.GetIDer, I groupsItemer](
 		// deleted and then restored will have a different ID than they did
 		// originally.
 		for remove := range removed {
-			delete(added, remove)
+			delete(addAndRem.Added, remove)
 		}
 
 		edc := NewCollection(
@@ -211,7 +209,7 @@ func populateCollections[C graph.GetIDer, I groupsItemer](
 				cl),
 			bh,
 			qp.ProtectedResource.ID(),
-			added,
+			addAndRem.Added,
 			removed,
 			c,
 			statusUpdater)

src/internal/m365/collection/groups/collection.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/alcionai/clues"
 	kjson "github.com/microsoft/kiota-serialization-json-go"
@@ -20,14 +21,14 @@ import (
 	"github.com/alcionai/corso/src/pkg/services/m365/api/graph"
 )
 
-var _ data.BackupCollection = &Collection[graph.GetIDer, groupsItemer]{}
+var _ data.BackupCollection = &prefetchCollection[graph.GetIDer, groupsItemer]{}
 
 const (
 	collectionChannelBufferSize = 1000
 	numberOfRetries             = 4
 )
 
-type Collection[C graph.GetIDer, I groupsItemer] struct {
+type prefetchCollection[C graph.GetIDer, I groupsItemer] struct {
 	data.BaseCollection
 	protectedResource string
 	stream            chan data.Item
@@ -35,7 +36,7 @@ type Collection[C graph.GetIDer, I groupsItemer] struct {
 	contains container[C]
 
 	// added is a list of existing item IDs that were added to a container
-	added map[string]struct{}
+	added map[string]time.Time
 	// removed is a list of item IDs that were deleted from, or moved out, of a container
 	removed map[string]struct{}
 
@@ -54,12 +55,12 @@ func NewCollection[C graph.GetIDer, I groupsItemer](
 	baseCol data.BaseCollection,
 	getAndAugment getItemAndAugmentInfoer[C, I],
 	protectedResource string,
-	added map[string]struct{},
+	added map[string]time.Time,
 	removed map[string]struct{},
 	contains container[C],
 	statusUpdater support.StatusUpdater,
-) Collection[C, I] {
+) prefetchCollection[C, I] {
-	collection := Collection[C, I]{
+	collection := prefetchCollection[C, I]{
 		BaseCollection:    baseCol,
 		added:             added,
 		contains:          contains,
@@ -75,7 +76,7 @@ func NewCollection[C graph.GetIDer, I groupsItemer](
 
 // Items utility function to asynchronously execute process to fill data channel with
 // M365 exchange objects and returns the data channel
-func (col *Collection[C, I]) Items(ctx context.Context, errs *fault.Bus) <-chan data.Item {
+func (col *prefetchCollection[C, I]) Items(ctx context.Context, errs *fault.Bus) <-chan data.Item {
 	go col.streamItems(ctx, errs)
 	return col.stream
 }
@@ -84,7 +85,7 @@ func (col *Collection[C, I]) Items(ctx context.Context, errs *fault.Bus) <-chan
 // items() production
 // ---------------------------------------------------------------------------
 
-func (col *Collection[C, I]) streamItems(ctx context.Context, errs *fault.Bus) {
+func (col *prefetchCollection[C, I]) streamItems(ctx context.Context, errs *fault.Bus) {
 	var (
 		streamedItems int64
 		totalBytes    int64
@@ -212,9 +213,9 @@ func (col *Collection[C, I]) streamItems(ctx context.Context, errs *fault.Bus) {
 	wg.Wait()
 }
 
-// finishPopulation is a utility function used to close a Collection's data channel
+// finishPopulation is a utility function used to close a collection's data channel
 // and to send the status update through the channel.
-func (col *Collection[C, I]) finishPopulation(
+func (col *prefetchCollection[C, I]) finishPopulation(
 	ctx context.Context,
 	streamedItems, totalBytes int64,
 	err error,

src/internal/m365/collection/groups/collection_test.go

@@ -162,7 +162,7 @@ func (getAndAugmentChannelMessage) augmentItemInfo(*details.GroupsInfo, models.C
 	// no-op
 }
 
-func (suite *CollectionUnitSuite) TestCollection_streamItems() {
+func (suite *CollectionUnitSuite) TestPrefetchCollection_streamItems() {
 	var (
 		t             = suite.T()
 		start         = time.Now().Add(-1 * time.Second)
@@ -177,26 +177,22 @@ func (suite *CollectionUnitSuite) TestCollection_streamItems() {
 
 	table := []struct {
 		name    string
-		added   map[string]struct{}
+		added   map[string]time.Time
 		removed map[string]struct{}
 	}{
 		{
-			name:    "no items",
+			name: "no items",
-			added:   map[string]struct{}{},
-			removed: map[string]struct{}{},
 		},
 		{
 			name: "only added items",
-			added: map[string]struct{}{
+			added: map[string]time.Time{
 				"fisher":    {},
 				"flannigan": {},
 				"fitzbog":   {},
 			},
-			removed: map[string]struct{}{},
 		},
 		{
-			name:  "only removed items",
+			name: "only removed items",
-			added: map[string]struct{}{},
 			removed: map[string]struct{}{
 				"princess": {},
 				"poppy":    {},
@@ -204,8 +200,10 @@ func (suite *CollectionUnitSuite) TestCollection_streamItems() {
 			},
 		},
 		{
-			name:  "added and removed items",
+			name: "added and removed items",
-			added: map[string]struct{}{},
+			added: map[string]time.Time{
+				"goblin": {},
+			},
 			removed: map[string]struct{}{
 				"general":  {},
 				"goose":    {},
@@ -224,7 +222,7 @@ func (suite *CollectionUnitSuite) TestCollection_streamItems() {
 			ctx, flush := tester.NewContext(t)
 			defer flush()
 
-			col := &Collection[models.Channelable, models.ChatMessageable]{
+			col := &prefetchCollection[models.Channelable, models.ChatMessageable]{
 				BaseCollection: data.NewBaseCollection(
 					fullPath,
 					nil,