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/gallery.go

@@ -6,12 +6,12 @@ import (
 	"errors"
 	"fmt"
 	"path/filepath"
+	"slices"
 
 	"github.com/doug-martin/goqu/v9"
 	"github.com/doug-martin/goqu/v9/exp"
 	"github.com/jmoiron/sqlx"
 	"github.com/stashapp/stash/pkg/models"
-	"github.com/stashapp/stash/pkg/sliceutil"
 	"gopkg.in/guregu/null.v4"
 	"gopkg.in/guregu/null.v4/zero"
 )
@@ -412,7 +412,7 @@ func (qb *GalleryStore) FindMany(ctx context.Context, ids []int) ([]*models.Gall
 		}
 
 		for _, s := range unsorted {
-			i := sliceutil.Index(ids, s.ID)
+			i := slices.Index(ids, s.ID)
 			galleries[i] = s
 		}