accounting: add context to Account and propagate changes #3257

This is preparation for getting the Accounting to check the context,
buf first we need to get it in place. Since this is one of those
changes that makes lots of noise, this is in a seperate commit.

vfs/vfscache/downloaders/downloaders.go

@@ -495,7 +495,7 @@ func (dl *downloader) open(offset int64) (err error) {
 	if err != nil {
 		return errors.Wrap(err, "vfs reader: failed to open source file")
 	}
-	dl.in = dl.tr.Account(in0).WithBuffer() // account and buffer the transfer
+	dl.in = dl.tr.Account(dl.dls.ctx, in0).WithBuffer() // account and buffer the transfer
 
 	dl.offset = offset