chore(llms): add vitest unit tests for llms package

packages/llms/vitest.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+	test: {
+		name: 'llms',
+		include: ['src/**/*.test.ts'],
+		// Suppress console output from passing tests; failed tests still get their logs.
+		silent: 'passed-only',
+	},
+})