fix: adding bufferutil as an optional dep (#1279)

# why

there was an issue with the alex ai endpoint deploying to vercel, where
while using stagehand v3 the scripts would correctly deploy and build,
but we weren't able to use them due to some bug where ws (websocket)
library would need bufferutil library to run any stagehand code
properly.

# what changed

added bufferutil library as an optional dep:
https://www.npmjs.com/package/bufferutil

# test plan

ci

Author: Kylejeong2

packages/core/package.json

@@ -72,6 +72,7 @@
     "@ai-sdk/togetherai": "^1.0.23",
     "@ai-sdk/xai": "^2.0.26",
     "@langchain/core": "^0.3.40",
+    "bufferutil": "^4.0.9",
     "chrome-launcher": "^1.2.0",
     "ollama-ai-provider-v2": "^1.5.0",
     "patchright-core": "^1.55.2",