Playground and add more demos

[boundless-forest]

Currently, there is only one number counter demo in this repository. It serves as a simple example for beginners. However, it would be beneficial to add more demos, such as token transfer, nft transfer, etc to showcase the capabilities of the Msgport. These additional demos should be both easy to understand and practical, providing useful functionality. Welcome to write your ideas in the issue section.

[boundless-forest]

Playground examples:

• https://play.rust-lang.org/?version=stable&mode=debug&edition=2021
• https://repl.axiom.xyz/

[boundless-forest]

https://github.com/msgport/msgport-examples/pull/6