feat: add copy button for Shiki Magic Move code block

[elecmonkey]

Added copy button support for Shiki Magic Move code block.

Add new configuration for slides - magicMoveCopy:

• false: Disable copy button
• 'final': Show copy button only on the final step
• true/'always': Show copy button on all steps (default)

Copy button in magic move code block respects the global codeCopy setting (if codeCopy is disabled, the magic move copy button will always be hidden) and it copies the current step's code content.

Hope this helps!

Closes #2255

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commit: 1eca0e7