fix(node): Prevent duplicate LangChain spans from double module patching

[github-actions]

Note

The pull request "fix(node): Prevent duplicate LangChain spans from double module patching " was created by @nicohrubec but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

The LangChain instrumentation registers both a module-level and a file-level hook for each provider package (e.g. @langchain/openai). Both hooks call _patch, which wraps the same prototype methods (invoke, stream, batch) with a new
proxy and callback handler. This results in every LangChain call producing duplicate gen_ai.chat spans. The fix adds a __sentry_patched__ guard on the prototype to skip patching if it's already been done.

[linear-code]

JS-1883

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #19684, which was included in the 10.43.0 release.