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

cmd/serve/s3/utils.go

@@ -36,7 +36,7 @@ func getDirEntries(prefix string, VFS *vfs.VFS) (vfs.Nodes, error) {
 	return dirEntries, nil
 }
 
-func getFileHashByte(node interface{}) []byte {
+func getFileHashByte(node any) []byte {
 	b, err := hex.DecodeString(getFileHash(node))
 	if err != nil {
 		return nil
@@ -44,7 +44,7 @@ func getFileHashByte(node interface{}) []byte {
 	return b
 }
 
-func getFileHash(node interface{}) string {
+func getFileHash(node any) string {
 	var o fs.Object
 
 	switch b := node.(type) {