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

lib/structs/structs.go

@@ -17,12 +17,12 @@ import (
 // This is useful for copying between almost identical structures that
 // are frequently present in auto-generated code for cloud storage
 // interfaces.
-func SetFrom(a, b interface{}) {
+func SetFrom(a, b any) {
 	ta := reflect.TypeOf(a).Elem()
 	tb := reflect.TypeOf(b).Elem()
 	va := reflect.ValueOf(a).Elem()
 	vb := reflect.ValueOf(b).Elem()
-	for i := 0; i < tb.NumField(); i++ {
+	for i := range tb.NumField() {
 		bField := vb.Field(i)
 		tbField := tb.Field(i)
 		name := tbField.Name
@@ -41,12 +41,12 @@ func SetFrom(a, b interface{}) {
 // This copies the public members only from b to a.  This is useful if
 // you can't just use a struct copy because it contains a private
 // mutex, e.g. as http.Transport.
-func SetDefaults(a, b interface{}) {
+func SetDefaults(a, b any) {
 	pt := reflect.TypeOf(a)
 	t := pt.Elem()
 	va := reflect.ValueOf(a).Elem()
 	vb := reflect.ValueOf(b).Elem()
-	for i := 0; i < t.NumField(); i++ {
+	for i := range t.NumField() {
 		aField := va.Field(i)
 		// Set a from b if it is public
 		if aField.CanSet() {