Reading poses in parallel multithreaded may cause errors

[AmitMY]

Followup from sign-language-processing/spoken-to-signed-translation#46

It seems like reading poses in parallel may result in errors.

https://github.com/sign-language-processing/spoken-to-signed-translation/blob/21a34fbb7ae6439eb8ed54b0c4a2a5c4538a7977/spoken_to_signed/gloss_to_pose/lookup/lookup.py#L111-L130

We should add a test