Idiomatic process for handling needed external language modules for which there is no port

[Joshua Root]

> How do you do package management on MacPorts for languages which might
> need modules which MacPorts doesn't have?
>
>    This problem exists for many languages supported by MacPorts; ie:
> Perl, Python, Raku, Julia, etc

The answer is different for each language. For Python, standard 
procedure is to use venv. <https://docs.python.org/3/library/venv.html>

I would assume for perl that if there isn't an equivalent mechanism, 
cpan should at least have an option to choose a different installation 
prefix. I don't know what the situation is for Raku and Julia.

- Josh