Pass cached variables explicitly instead of through env vars

[n-p-e]

Description

Pass cached variables explicitly instead of through env vars, instead of exposing them to all processes launched by the shell.

Closes #600

Screenshots (if appropriate)

How Has This Been Tested

• Normal prompt (including git status) works

• Unit tests run

• [x] I have tested using Linux.

• [x] I have tested using MacOS.

Checklist

• [ ] I am ready to update the wiki accordingly.
• [ ] I have updated the tests accordingly.