Deprecate implicit tuple construction in yieldAsync

It was a bad idea from the start. Regular `yield` statement in Nim does
not accept multiple values - why should we? A DSL should mimic the
syntax and semantics as close as possible. Being more permissive is
still a deviation from the original, which increases cognitive load.

src/asyncIters/private/asyncIter.nim

@@ -72,7 +72,8 @@ type Inaccessible = object
 template yieldAsync*(phantom: Inaccessible)
   {.error: "congratulations, you've found a way to invoke me".} = discard
 
-macro yieldAsync*(values: varargs[typed]): untyped =
+macro yieldAsync*(values: varargs[typed]): untyped
+    {.deprecated: "enclose multiple values in parentheses to yield them as a tuple".} =
   ## Transfer control to the caller of the async iterator. If several values are passed, they
   ## are wrapped in a tuple.
   case values.len:

tests/test.nim

@@ -88,11 +88,9 @@ proc main =
   test "`awaitIter` can unpack simple tuples":
     asyncIter:
       iterator indexedStrings: Future[(int, string)] =
-        yieldAsync 1, "test"
         yieldAsync (1, "test")
 
       iterator indexedPositions: Future[(int, string, tuple[x, y: float])] =
-        yieldAsync 1, "here", (2.0, 4.0)
         yieldAsync (1, "here", (2.0, 4.0))
 
     var n = 0
@@ -114,7 +112,7 @@ proc main =
         check x == 2.0
         check y == 4.0
         n += 1
-    check n == 8
+    check n == 4
 
   test "`awaitIter` can unpack a 1-element tuple":
     asyncIter: