build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

backend/ulozto/api/types.go

@@ -82,8 +82,8 @@ type File struct {
 	ContentType              string `json:"content_type"`
 	Format                   struct {
 	} `json:"format"`
-	DownloadTypes []interface{} `json:"download_types"`
-	ThumbnailInfo []interface{} `json:"thumbnail_info"`
+	DownloadTypes []any `json:"download_types"`
+	ThumbnailInfo []any `json:"thumbnail_info"`
 	PreviewInfo   struct {
 	} `json:"preview_info"`
 	Privacy          string    `json:"privacy"`

backend/ulozto/ulozto.go

@@ -729,7 +729,7 @@ func (o *Object) Storable() bool {
 	return true
 }
 
-func (o *Object) updateFileProperties(ctx context.Context, req interface{}) (err error) {
+func (o *Object) updateFileProperties(ctx context.Context, req any) (err error) {
 	var resp *api.File
 
 	opts := rest.Opts{
@@ -887,7 +887,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 
 // Remove implements the mandatory method fs.Object.Remove
 func (o *Object) Remove(ctx context.Context) error {
-	for i := 0; i < 2; i++ {
+	for range 2 {
 		// First call moves the item to recycle bin, second deletes it for good
 		var err error
 		opts := rest.Opts{