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/sync/pipe_test.go

@@ -114,11 +114,11 @@ func TestPipeConcurrent(t *testing.T) {
 	ctx := context.Background()
 	var count atomic.Int64
 
-	for j := 0; j < readWriters; j++ {
+	for range readWriters {
 		wg.Add(2)
 		go func() {
 			defer wg.Done()
-			for i := 0; i < N; i++ {
+			for range N {
 				// Read from pipe
 				pair2, ok := p.Get(ctx)
 				assert.Equal(t, pair1, pair2)
@@ -128,7 +128,7 @@ func TestPipeConcurrent(t *testing.T) {
 		}()
 		go func() {
 			defer wg.Done()
-			for i := 0; i < N; i++ {
+			for range N {
 				// Put an object
 				ok := p.Put(ctx, pair1)
 				assert.Equal(t, true, ok)