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

backend/cache/handle.go

@@ -182,7 +182,7 @@ func (r *Handle) queueOffset(offset int64) {
 			}
 		}
 
-		for i := 0; i < r.workers; i++ {
+		for i := range r.workers {
 			o := r.preloadOffset + int64(r.cacheFs().opt.ChunkSize)*int64(i)
 			if o < 0 || o >= r.cachedObject.Size() {
 				continue
@@ -222,7 +222,7 @@ func (r *Handle) getChunk(chunkStart int64) ([]byte, error) {
 	if !found {
 		// we're gonna give the workers a chance to pickup the chunk
 		// and retry a couple of times
-		for i := 0; i < r.cacheFs().opt.ReadRetries*8; i++ {
+		for i := range r.cacheFs().opt.ReadRetries * 8 {
 			data, err = r.storage().GetChunk(r.cachedObject, chunkStart)
 			if err == nil {
 				found = true