Enhance the code block elements - Close the block as its generated and add a copy button.

[Art9681]

The current implementation does not correctly format large code blocks as they are being generated due to the closing tag not being generated by LLM. We need a method to close the blocks as the code is being generated so they display properly from the start.

We also need a copy button on the top right of the block so the end user can easily copy the code.

The copy button will need to be implemented in the chat template:

https://github.com/intelligencedev/eternal/blob/main/public/templates/chat.html

[Art9681]

The code block fix was applied in #20

Leaving this Issue open until the copy button is implemented as that is a highly desired feature.