Animations: let 'Play' button support different durations for different frames

So far the button Play only support a single frame duration and a single transition duration for all the steps of the animation. It would be very useful to support different duration values at different frame step. Note that I haven't any way to define specific duration per frame, I am open to suggestions.

Current:

fig.update_layout(
    updatemenus=[{
        'type': 'buttons',
        'buttons': [
            {
                'label': 'Play',
                'method': 'animate',
                'args': [None, {
                    'fromcurrent': True,
                    'frame': {'duration': 100, 'redraw': False},
                    'transition': {'duration': 100}
                }]
            }
        ]
    }]
)

Possible alternative way to pass information:

fig.update_layout(
    updatemenus=[{
        'type': 'buttons',
        'buttons': [
            {
                'label': 'Play',
                'method': 'animate',
                'args': [None, {
                    'fromcurrent': True,
                    'frame': [(str(i), {'duration': 100 if i%2 == 0 else 1000, 'redraw': False}) for i in range(len(frames))],
                    'transition': [(str(i), {'duration': 100 if i%2 == 0 else 1000}) for i in range(len(frames))]
                }]
            }
        ]
    }]
)

从通过 fig.update_layout 传入的动画配置开始，尤其关注使用 method animate 和 args 的 updatemenus 按钮。跟踪 frame 和 transition 时长是如何被解释的，然后定义并测试一种方式，使 Play 使用每帧的值，同时保留当前的单时长形式。