Move copy code buttons to JavaScript for better RSS feed compatibility

[imfing]

Currently, the "copy code" buttons are created in advance and included directly in the HTML. This approach has a downside: it adds SVG icons to every code block, which messes up how the RSS feed looks.

hextra/layouts/_default/_markup/render-codeblock.html

Lines 18 to 21 in 2df3c56

	<button class="code-copy-btn group/copybtn transition-all active:opacity-50 bg-primary-700/5 border border-black/5 text-gray-600 hover:text-gray-900 rounded-md p-1.5 dark:bg-primary-300/10 dark:border-white/10 dark:text-gray-400 dark:hover:text-gray-50" title="Copy code" data-clipboard-target="#code-block-{{ .Ordinal }}">
	{{ partial "utils/icon.html" (dict "name" "copy" "attributes" "class=\"group-[.copied]/copybtn:hidden pointer-events-none h-4 w-4\"") }}
	{{ partial "utils/icon.html" (dict "name" "check" "attributes" "class=\"hidden group-[.copied]/copybtn:block success-icon pointer-events-none h-4 w-4\"") }}
	</button>

A better way to handle this is to shift the "copy code" button creation to the assets/js/code-copy.js file. By doing this, the buttons get added dynamically when the page loads, avoiding any issues with the RSS feed.