fix: asof_join doc group :join → :joins (#31)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cigrainger

lib/dux.ex

@@ -1218,7 +1218,7 @@ defmodule Dux do
     %{left | ops: ops ++ [{:join, right, how, on_cols, suffix}]}
   end
 
-  @doc group: :join
+  @doc group: :joins
   @doc """
   ASOF join — match each left row to the nearest right row satisfying an inequality.