use transfer stages for copy --from

See commit e04a931439 for an explanation
of why move uses transfer stages for --from, but command stages for
--to. At the point of that commit, copy was actually already using
command stages for everything, so the commit was incorrect about
improving copy --to.

But, the same reasoning about --from applies to copy as to move; when
verification is not done incrementally, download and verification are
the main two stages. The cleanup stage for copy is even less work than
for move (it doesn't drop from the remote).

Sponsored-by: Dartmouth College's DANDI project

Command/Copy.hs

@@ -50,7 +50,7 @@ seek o = case fromToOptions o of
 	Nothing -> giveup "Specify --from or --to"
 
 seek' :: CopyOptions -> FromToHereOptions -> CommandSeek
-seek' o fto = startConcurrend stages $ do
+seek' o fto = startConcurrency (Command.Move.stages fto) $ do
 	case batchOption o of
 		NoBatch -> withKeyOptions
 			(keyOptions o) (autoMode o) seeker
@@ -73,12 +73,6 @@ seek' o fto = startConcurrend stages $ do
 		}
 	keyaction = Command.Move.startKey fto Command.Move.RemoveNever
 
-	stages = case fto of
-		FromOrToRemote (FromRemote _) -> commandStages
-		FromOrToRemote (ToRemote _) -> commandStages
-		ToHere -> commandStages
-		FromRemoteToRemote _ _ -> transferStages
-
 {- A copy is just a move that does not delete the source file.
  - However, auto mode avoids unnecessary copies, and avoids getting or
  - sending non-preferred content. -}

Command/Move.hs

@@ -65,7 +65,7 @@ seek o = case fromToOptions o of
 	Nothing -> giveup "Specify --from or --to"
 
 seek' :: MoveOptions -> FromToHereOptions -> CommandSeek
-seek' o fto = startConcurrency stages $ do
+seek' o fto = startConcurrency (stages fto) $ do
 	case batchOption o of
 		NoBatch -> withKeyOptions (keyOptions o) False seeker
 			(commandAction . keyaction)
@@ -83,14 +83,15 @@ seek' o fto = startConcurrency stages $ do
 			FromRemoteToRemote _ _ -> Nothing
 		, usesLocationLog = True
 		}
-	stages = case fto of
-		FromOrToRemote (FromRemote _) -> transferStages
-		FromOrToRemote (ToRemote _) -> commandStages
-		ToHere -> transferStages
-		FromRemoteToRemote _ _ -> transferStages
 	keyaction = startKey fto (removeWhen o)
 	ww = WarnUnmatchLsFiles
 
+stages :: FromToHereOptions -> UsedStages
+stages (FromOrToRemote (FromRemote _)) = transferStages
+stages (FromOrToRemote (ToRemote _)) = commandStages
+stages ToHere = transferStages
+stages (FromRemoteToRemote _ _) = transferStages
+
 start :: FromToHereOptions -> RemoveWhen -> SeekInput -> RawFilePath -> Key -> CommandStart
 start fromto removewhen si f k = start' fromto removewhen afile si k ai
   where