[BUG] `{lang}` code blocks: `parentElement.className` is overwritten, wiping classes from other plugins

[heshuren371]

Describe the bug

When a code block uses the Rmd/Quarto-style language identifier (e.g. ```{python}), addToCodeBlock rewrites the classes of the parent <pre> element by assignment:

// src/RunButton.ts:126 (addToCodeBlock)
codeBlock.parentElement.className = codeBlock.className;

This replaces the entire class list of the <pre> instead of adding to it. Any classes previously added to the <pre> by Obsidian core or other plugins are silently removed.

To Reproduce

1. Install a plugin that decorates code blocks at the <pre> level (e.g. Code Styler, which adds code-styler-pre and fold-state classes).
2. Create a note with a ```{python} block.
3. Switch to reading mode.

Expected behavior

The plugin should only adjust the classes it needs (e.g. via classList.add / classList.replace), preserving classes set by Obsidian or other plugins.

Actual behavior

All pre-existing <pre> classes are wiped. Downstream effects observed with Code Styler (reported as mayurankv/Obsidian-Code-Styler#334):

• Code block styling and folding state are lost for {lang} blocks.
• The copy button ends up mis-positioned / broken because the CSS selectors that place it depend on the removed classes.
• Unload/cleanup routines of the other plugin can no longer find the block (pre.code-styler-pre selector misses), leaving stale header elements behind.

Suggested fix

// Instead of overwriting:
codeBlock.parentElement.className = codeBlock.className;
// Only add what's needed, e.g.:
codeBlock.classList.forEach((cls) => codeBlock.parentElement.classList.add(cls));

(or the minimal equivalent that adds the rewritten language-x { classes without clearing the rest.)

Environment

• Plugin version: 2.1.2
• Obsidian version: 1.8+
• OS: macOS (likely affects all platforms)