Use slices package from the stdlib when possible (#5360)

* Use slices from the stdlib when possible

* Add some unit tests

* More small tweaks + add benchmark func

pkg/sqlite/image.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"path/filepath"
+	"slices"
 
 	"github.com/jmoiron/sqlx"
 	"github.com/stashapp/stash/pkg/models"
@@ -398,7 +399,7 @@ func (qb *ImageStore) FindMany(ctx context.Context, ids []int) ([]*models.Image,
 		}
 
 		for _, s := range unsorted {
-			i := sliceutil.Index(ids, s.ID)
+			i := slices.Index(ids, s.ID)
 			images[i] = s
 		}