random cdisc data very slow for larger data

# Original message

Running the following code takes a long time! This is on r.roche.com, r 3.6.3

NEST/nest_on_bee/master/bee_nest_utils.R")
bee_use_nest(release = "2021_05_05")
ADSL <- radsl(N = 1002)
ADLB <- radlb(ADSL)

I reduced this from 15000 as it took way too long. Using system.time I get the following results:

user system elapsed
37.852 0.584 38.436

This is extremely long to make a dataset with 21,000 records! I know random.cdisc really only exists for dummy data, but this seems like extremely poor performance

Provenance:
```
Creator: martik32
```

# TODO

Improve performance. A few suggestion

1. use mclapply
2. datatable if necessary