eww: [BUG] Sliding animations don't work with revealer

Describe the bug

All slide animations just don’t work with the reveler widget, however, the fade animation works.

Reproducing the issue

1. Use this config

<eww>
    <windows>
        <window name="bar_window" stacking="fg" focusable="false">
            <geometry anchor="top left" x="0px" y="0px" width="100%" height="48px"/>
            <reserve side="left" distance="50px"/>
            <widget>
                <revealer transition="slideright" duration="1s" reveal="{{show}}">
                    <box hexpand="false">
                        <label text="lolololololol"/>
                    </box>
                </revealer>
            </widget>
        </window>
    </windows>
</eww>

1. eww daemon
2. eww open bar_window
3. eww update show=true As you can see the label shows instantly and without animation
4. eww update show=false As you can see the label hides abruptly after 1 second and without animation

Expected behaviour

I expect the sliding animations to work.