MacOS incompatibility

It seems the package has incompatibility because of missing `mremap` on darwin platform.

I would appreciate if you can look into it? There are multiple options:
- Maybe `mremap` can be replaced with `munmap` followed by `mmap`  with new size?
- Use mremap (and related mmap functions) available in newer version of GO https://pkg.go.dev/golang.org/x/sys@v0.16.0/unix#Mremap

