Replace brittle os.chdir usage in make.py with a context manager

[pushfoo]

Stacks onto #1725.

Changes

• Add simple context manager wrapping cd behavior
• Add helper constants
• Modify run to accept an optional cd path
• Add a helper run_doc function combining run with a constant
• Remove top-level os.chdir
• Remove brittle use of os.chdir('../') in command functions

This doesn't use a combined decorator function because typer interacts poorly with other decorators.

How to test

The important parts should be covered by this, run as a script or individually.

#!/bin/bash

python make.py html
python make.py clean
python make.py lint
python make.py test
python make.py serve
# Swap to your browser at this point per the in-terminal instructions.