limit amount of slot queue workers to 1

reason: proof generation does not happen in
separate threads yet, so to avoid taking too
long to provide initial storage proofs we only
pick up one slot at a time

codex/sales/slotqueue.nim

@@ -58,7 +58,7 @@ type
   QueueNotRunningError* = object of SlotQueueError
 
 # Number of concurrent workers used for processing SlotQueueItems
-const DefaultMaxWorkers = 3
+const DefaultMaxWorkers = 1
 
 # Cap slot queue size to prevent unbounded growth and make sifting more
 # efficient. Max size is not equivalent to the number of slots a host can

tests/codex/sales/testsales.nim

@@ -311,7 +311,7 @@ asyncchecksuite "Sales":
     createAvailability() # enough to fill a single slot
     await market.requestStorage(request)
     let items = SlotQueueItem.init(request)
-    await sleepAsync(10.millis) # queue starts paused, allow items to be added to the queue
+    await allowRequestToStart()
     check eventually queue.paused
     # The first processed item/slot will be filled (eventually). Subsequent
     # items will be processed and eventually re-pushed with `seen = true`. Once