How to map simple key chords like emacs?

In emacs editor, we can type "f", "j" individually and they will appear in the editor.

However if we create a key chord mapping for "fj" and press them at once, it will invoke a corresponding action.

```
(key-chord-define-global "fj" 'undo)
```

How to achieve a similar simple key chord with skhd?

No files, tests, or entry points are mentioned. Start by reviewing skhd's existing key-mapping documentation and determine whether it supports multi-key chords while preserving individual key input. Done means providing a confirmed configuration approach or clarifying the feature needed to support this behavior.

Written by the indexing model from the issue text.