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/kv/internal_test.go

@@ -20,7 +20,7 @@ func TestKvConcurrency(t *testing.T) {
 	ctx := context.Background()
 	results := make([]*DB, threadNum)
 	wg.Add(threadNum)
-	for i := 0; i < threadNum; i++ {
+	for i := range threadNum {
 		go func(i int) {
 			db, err := Start(ctx, "test", nil)
 			require.NoError(t, err)
@@ -35,11 +35,11 @@ func TestKvConcurrency(t *testing.T) {
 	db := results[0]
 	assert.Equal(t, 1, len(dbMap))
 	assert.Equal(t, threadNum, db.refs)
-	for i := 0; i < threadNum; i++ {
+	for i := range threadNum {
 		assert.Equal(t, db, results[i])
 	}
 
-	for i := 0; i < threadNum; i++ {
+	for i := range threadNum {
 		assert.Equal(t, 1, len(dbMap))
 		err := db.Stop(false)
 		assert.NoError(t, err, "unexpected error %v at retry %d", err, i)
@@ -54,7 +54,7 @@ func TestKvExit(t *testing.T) {
 	require.Equal(t, 0, len(dbMap), "no databases can be started initially")
 	const dbNum = 5
 	ctx := context.Background()
-	for i := 0; i < dbNum; i++ {
+	for i := range dbNum {
 		facility := fmt.Sprintf("test-%d", i)
 		for j := 0; j <= i; j++ {
 			db, err := Start(ctx, facility, nil)