Fix Fireworks Callbacks (#12003)
I may be missing something but it seems like we inappropriately overrode
the 'stream()' method, losing callbacks in the process. I don't think
(?) it gave us anything in this case to customize it here?
See new trace:
https://smith.langchain.com/public/fbb82825-3a16-446b-8207-35622358db3b/r
and confirmed it streams.
Also fixes the stopwords issues from #12000
