nPhase has no option to set max heterozygosity level

[OmarOakheart]

Whenever someone wants to run nPhase on a very heterozygous, large genome and runs into memory issues/takes too long to run, I recommend subsampling the vcf down to a 0.5~1% heterozygosity level since nPhase will still perform well (and significantly faster). This is probably a pain for everyone and it would be good to include an option to set a maximum heterozygosity level so that the pipeline can do the subsampling it on its own.