Fixed the issue that theme-switch does not work on docs.

packages/mermaid/src/docs/.vitepress/theme/mermaid.ts

@@ -8,7 +8,9 @@ try {
 }
 
 export const render = async (id: string, code: string, config: MermaidConfig): Promise<string> => {
-  mermaid.initialize(config);
+  // make a clone of config, so we don't mutate the original
+  const mermaidConfig = { ...config };
+  mermaid.initialize(mermaidConfig);
   const svg = await mermaid.renderAsync(id, code);
   return svg;
 };