Add get_clipboard and set_clipboard to session.

[16amattice]

What does it do?

This PR adds the ability to interact with the client's clipboard in the Rio framework. Specifically, it introduces two new methods:

• set_clipboard to set the clipboard text
• get_clipboard to retrieve the current clipboard text

Why is it needed?

Clipboard operations enhance user experience by allowing easy copying and pasting of text programmatically.

How to test it?

1. Environment: Ensure you have the development environment set up with the Rio framework.
2. Path to Verify:
   • Create buttons in your test app with on_press events.
   • Use self.session.set_clipboard and self.session.get_clipboard in these event handlers.
   • Click the buttons to test clipboard functionality.

Related issue(s)/PR(s)

None

[Aran-Fey]

Great work! Just one thing: According to MDN, navigator.clipboard is only available in certain situations. Could you add a ClipboardError that's raised when the browser doesn't support navigator.clipboard?