[tui] add animation support, and animated gradient support

[nazmulidris]

Before r3bl-cmdr alpha release, implement easy support for animation (currently this is supported, but provide a nice API to make this simple).

Take a look at this code for inspiration:

https://github.com/r3bl-org/r3bl_rs_utils/blob/main/tui/examples/demo/ex_rc/launcher.rs#L23

And formalize the patterns above into reusable:

• Animated clock

• Animated gradient for dialog box border

  

Think about animating the caret when the user stops moving it. Perhaps consider animating the cursor when it first appears like in a dialog box. Animation doesn't just have to be for ambient effects.

Here's a great video to draw inspiration from for ideas on animations at 11:25 timestamp
https://youtu.be/TbZ3HzvFEto?si=Ab9-IFx7ms4IfUF6