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/mmap/mmap_test.go

@@ -47,7 +47,7 @@ func BenchmarkAllocFree(b *testing.B) {
 func BenchmarkAllocFreeWithLotsOfAllocations(b *testing.B) {
 	const size = 4096
 	alloc := func(n int) (allocs [][]byte) {
-		for i := 0; i < n; i++ {
+		for range n {
 			mem := MustAlloc(size)
 			mem[0] ^= 0xFF
 			allocs = append(allocs, mem)
@@ -76,7 +76,7 @@ func BenchmarkAllocFreeWithLotsOfAllocations(b *testing.B) {
 func BenchmarkAllocFreeForLotsOfAllocations(b *testing.B) {
 	const size = 4096
 	alloc := func(n int) (allocs [][]byte) {
-		for i := 0; i < n; i++ {
+		for range n {
 			mem := MustAlloc(size)
 			mem[0] ^= 0xFF
 			allocs = append(allocs, mem)