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/asyncreader/asyncreader.go

@@ -75,7 +75,7 @@ func (a *AsyncReader) init(rd io.ReadCloser, buffers int) {
 	a.size = softStartInitial
 
 	// Create tokens
-	for i := 0; i < buffers; i++ {
+	for range buffers {
 		a.token <- struct{}{}
 	}
 
@@ -249,10 +249,7 @@ func (a *AsyncReader) SkipBytes(skip int) (ok bool) {
 			}
 		}
 
-		n := len(a.cur.buffer())
-		if n > skip {
-			n = skip
-		}
+		n := min(len(a.cur.buffer()), skip)
 		a.cur.increment(n)
 		skip -= n
 		if skip == 0 {