Add "Copy to Clipboard" Feature for Message Markdown

[IberAI]

This pull request introduces a feature that allows users to copy the markdown of a message directly to the system clipboard, addressing the functionality requested in issue #10.

Features Implemented:

• A keybind (c) has been set up to copy the markdown content of a focused message.
• Utilizes pyperclip for cross-platform clipboard interaction. See documentation

Development Notes:

• The feature has been manually tested on multiple environments to ensure compatibility.
• Further integration tests can be set up to automate testing across different systems.

Usage:

• Focus on a message within the application.
• Press c to copy the message markdown to the clipboard.

By resolving issue #10, this enhancement significantly improves user interactivity and efficiency in copying content for documentation or sharing purposes. Related issue: #10

[darrenburns]

Hey, thanks for this PR. Unfortunately it came at a time where I was in the middle of a complete rewrite (version 1.0) of Elia, which has now been released.

There's now support for copying and you can select parts of a message to copy too. It's done via a terminal protocol which has decent support.