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/http/middleware_test.go

@@ -78,7 +78,7 @@ func TestMiddlewareAuth(t *testing.T) {
 			},
 			auth: AuthConfig{
 				Realm: "test",
-				CustomAuthFn: func(user, pass string) (value interface{}, err error) {
+				CustomAuthFn: func(user, pass string) (value any, err error) {
 					if user == "custom" && pass == "custom" {
 						return true, nil
 					}
@@ -294,7 +294,7 @@ func TestMiddlewareAuthCertificateUser(t *testing.T) {
 			},
 			auth: AuthConfig{
 				Realm: "test",
-				CustomAuthFn: func(user, pass string) (value interface{}, err error) {
+				CustomAuthFn: func(user, pass string) (value any, err error) {
 					if user == "custom" && pass == "custom" {
 						return true, nil
 					}
@@ -316,7 +316,7 @@ func TestMiddlewareAuthCertificateUser(t *testing.T) {
 			},
 			auth: AuthConfig{
 				Realm: "test",
-				CustomAuthFn: func(user, pass string) (value interface{}, err error) {
+				CustomAuthFn: func(user, pass string) (value any, err error) {
 					fmt.Println("CUSTOMAUTH", user, pass)
 					if user == "rclone-dev-client" && pass == "" {
 						return true, nil