test: fix "Failed to parse ... TimecodesPlugin.ts" error

Fix "Failed to parse ... TimecodesPlugin.ts" error by creating virtual module for 'obsidian' package.

Related discussion: vitest-dev/vitest#9298

vitest.config.ts

@@ -1,6 +1,24 @@
 import { defineConfig } from 'vitest/config'
 
 export default defineConfig({
+  plugins: [
+    {
+      name: 'virtual-obsidian',
+      enforce: 'pre',
+      resolveId(id) {
+        if (id === 'obsidian') {
+          return '\0obsidian'
+        }
+      },
+      load(id) {
+        if (id === '\0obsidian') {
+          return `
+            export class Plugin {}
+            export default {}`
+        }
+      },
+    },
+  ],
   test: {
     isolate: false,
     pool: 'threads',