refactor: Move scroller into own testable module

lua/telescope/pickers/scroller.lua

@@ -0,0 +1,34 @@
+
+local scroller = {}
+
+scroller.create = function(strategy)
+  if strategy == 'cycle' then
+    return function(max_results, num_results, row)
+      local count = math.min(max_results, num_results)
+
+      if row >= count then
+        return 0
+      elseif row < 0 then
+        return count - 1
+      end
+
+      return row
+    end
+  elseif strategy == 'limit' or strategy == nil then
+    return function(max_results, num_results, row)
+      local count = math.min(max_results, num_results)
+
+      if row >= count then
+        return count - 1
+      elseif row < 0 then
+        return 0
+      end
+
+      return row
+    end
+  else
+    error("Unsupported strategy: ", strategy)
+  end
+end
+
+return scroller