set number of threads with env variable

Hi, is there an issue to confine the max number of threads with env variable?
Same as done for other packages:
e.g.:
```
export OMP_NUM_THREADS=1
export MKL_NUM_THREADS=1
export NUMEXPR_NUM_THREADS=1
```
([I know it is possible directly in python](https://www.blosc.org/python-blosc2/reference/autofiles/low_level/blosc2.set_nthreads.html), but sometimes it is easier in bash) 
Thanks,