Deprecate cycle and repeat

Deprecate `Data.List.Linear.cycle` and `Data.List.Linear.repeat`.
Infinite results cannot be consumed linearly, so they are not really
useful in a linear context. They could be consumed by a program that
exits via an exception, but I don't think that's something that should
really be supported.

Begins to address tweag#453

src/Data/List/Linear.hs

@@ -289,9 +289,11 @@ iterate f a =
   dup2 a & \(a', a'') ->
     a' : iterate f (f a'')
 
+{-# DEPRECATED repeat "The result cannot be consumed linearly, so this function is not useful." #-}
 repeat :: (Dupable a) => a %1 -> [a]
 repeat = iterate id
 
+{-# DEPRECATED cycle "The result cannot be consumed linearly, so this function is not useful." #-}
 cycle :: (HasCallStack, Dupable a) => [a] %1 -> [a]
 cycle [] = Prelude.error "cycle: empty list"
 cycle xs = dup2 xs & \(xs', xs'') -> xs' ++ cycle xs''