mv_extract_exposures runs too slow when the number of instruments is large

[YuxiaoRuoyao]

The mv_extract_exposures() function will run for a long time when there are about 400 instruments or more, and sometimes it will get time out.
For example: dat <-mv_extract_exposures(c("ebi-a-GCST90029070","ebi-a-GCST90002363","ukb-b-19953"))
I think the main stucking step is at the line:
d1 <- extract_outcome_data(exposure_dat$SNP, id_exposure, opengwas_jwt = opengwas_jwt, proxies = find_proxies)
I see actually you have the parameters for splitting chunks and smaller number of splitsize() may help to speed up since that will make the access by api faster. Is this a correct way to improve that? If so, could you add this parameter in mv_extract_exposures() function for changing the splitsize?

Thank you!