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

fs/config/configstruct/configstruct.go

@@ -35,7 +35,7 @@ func camelToSnake(in string) string {
 //
 // Any other types are expected to be encoded by their String()
 // methods and decoded by their `Set(s string) error` methods.
-func StringToInterface(def interface{}, in string) (newValue interface{}, err error) {
+func StringToInterface(def any, in string) (newValue any, err error) {
 	typ := reflect.TypeOf(def)
 	o := reflect.New(typ)
 	switch def.(type) {
@@ -88,10 +88,10 @@ func StringToInterface(def interface{}, in string) (newValue interface{}, err er
 
 // Item describes a single entry in the options structure
 type Item struct {
-	Name  string            // snake_case
-	Field string            // CamelCase
-	Set   func(interface{}) // set this field
-	Value interface{}
+	Name  string    // snake_case
+	Field string    // CamelCase
+	Set   func(any) // set this field
+	Value any
 }
 
 // Items parses the opt struct and returns a slice of Item objects.
@@ -105,7 +105,7 @@ type Item struct {
 // Nested structs are looked up too. If the parent struct has a struct
 // tag, this will be used as a prefix for the values in the sub
 // struct, otherwise they will be embedded as they are.
-func Items(opt interface{}) (items []Item, err error) {
+func Items(opt any) (items []Item, err error) {
 	def := reflect.ValueOf(opt)
 	if def.Kind() != reflect.Ptr {
 		return nil, errors.New("argument must be a pointer")
@@ -115,7 +115,7 @@ func Items(opt interface{}) (items []Item, err error) {
 		return nil, errors.New("argument must be a pointer to a struct")
 	}
 	defType := def.Type()
-	for i := 0; i < def.NumField(); i++ {
+	for i := range def.NumField() {
 		field := def.Field(i)
 		fieldType := defType.Field(i)
 		fieldName := fieldType.Name
@@ -145,7 +145,7 @@ func Items(opt interface{}) (items []Item, err error) {
 			defaultItem := Item{
 				Name:  configName,
 				Field: fieldName,
-				Set: func(newValue interface{}) {
+				Set: func(newValue any) {
 					field.Set(reflect.ValueOf(newValue))
 				},
 				Value: field.Interface(),
@@ -169,7 +169,7 @@ func Items(opt interface{}) (items []Item, err error) {
 // types and set in opt.
 //
 // All the field types in the struct must implement fmt.Scanner.
-func Set(config configmap.Getter, opt interface{}) (err error) {
+func Set(config configmap.Getter, opt any) (err error) {
 	defaultItems, err := Items(opt)
 	if err != nil {
 		return err
@@ -177,7 +177,7 @@ func Set(config configmap.Getter, opt interface{}) (err error) {
 	for _, defaultItem := range defaultItems {
 		newValue := defaultItem.Value
 		if configValue, ok := config.Get(defaultItem.Name); ok {
-			var newNewValue interface{}
+			var newNewValue any
 			newNewValue, err = StringToInterface(newValue, configValue)
 			if err != nil {
 				// Mask errors if setting an empty string as