Add nushell support for Lmod

[MilesCranmer]

Here is an implementation of nushell support per the discussion in #704. This builds off of @rtmclay's branch IS704.

FYI have only done simple tests of this in a docker image but haven't tested it in production yet (I am not a sysadmin on my institution's cluster).

Usage:

overlay use /path/to/lmod/init/nushell
lmod-module load gcc
lmod-module list

(we can’t use module since this is a special keyword in nushell)

Fixes #704

[MilesCranmer]

Actually maybe I’ll push this to IS704 so the diff is cleaner. Let me update..

[MilesCranmer]

Quick update is it seems to work on the cluster too! I am loading cluster-maintained modules and see the env variables get updated correctly

[rtmclay]

I have merged in PR #784 into the main branch. I merged in everything but shell/Nushell.lua. It remains as it was:

1. $env.__LMOD_STACK variables are base64 encodes so there is no need to add r#'string'# quotes
2. The trailing comma in path like variables is necessary part of the regression testing system.

You can pull the main branch now to test this. This will be part of the next release of Lmod.

[rtmclay]

This PR with my changes as been released as Lmod 8.7.65.