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/putio/fs.go

@@ -332,10 +332,7 @@ func (f *Fs) sendUpload(ctx context.Context, location string, size int64, in io.
 	var offsetMismatch bool
 	buf := make([]byte, defaultChunkSize)
 	for clientOffset < size {
-		chunkSize := size - clientOffset
-		if chunkSize >= int64(defaultChunkSize) {
-			chunkSize = int64(defaultChunkSize)
-		}
+		chunkSize := min(size-clientOffset, int64(defaultChunkSize))
 		chunk := readers.NewRepeatableLimitReaderBuffer(in, buf, chunkSize)
 		chunkStart := clientOffset
 		reqSize := chunkSize