Unnecessary array allocation

`Array.from` call in `concat2` function creates a new temporary array which is used only to call `forEach`, it doesn't seem efficient. Why not to iterate `map2` itself with `for..of` syntax?

Locate the concat2 function and inspect the Array.from call that feeds forEach, along with how map2 is used. Replace the temporary-array iteration with direct iteration over map2 while preserving the existing concatenation behavior; verify the project's available checks after the change.

Written by the indexing model from the issue text.