Run tool calls in parallel

[jmoseley]

• [x] I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

Run tool calls in parallel, since they have no dependency on one another.

Additional context & links

https://github.com/openai/openai-node/issues/1131

[danfhernandez]

https://github.com/openai/openai-node/issues/1131

[atesgoral]

Parallelism maybe could be controlled by an option, since in some systems it could still be desirable to run tools exclusively, in parallel. (Though in those cases one can always throw in a mutex to gate function calls.)