Respect NUMEXPR_MAX_THREADS when setting numexpr thread count

[skmendez]

Avoid calling numexpr.set_num_threads() with a value exceeding NUMEXPR_MAX_THREADS to prevent numexpr from printing a warning to stderr during blosc2 import. Without this, I get the following error log from numexpr:

$ NUMEXPR_MAX_THREADS=16 python -c 'import blosc2; blosc2.__version__'
Error.  nthreads cannot be larger than environment variable "NUMEXPR_MAX_THREADS" (16)%

[FrancescAlted]

Thanks @skmendez . I am wondering if this patch would be better suited in numexpr package itself. Thoughts?

[skmendez]

I think it makes sense to warn if you attempt to set the number of threads to a value greater than NUMEXPR_MAX_THREADS (though I will say the error message not being new line terminated is pretty rough). My only wish is that numexpr exposed the "max threads" through a function instead of needing to query an env variable, but oh well :/