Package update + more docs on dev setup

[dmchoiboi]

Pull Request Summary

What is this PR changing? Why is this change being made? Any caveats you'd like to highlight? Link any relevant documents, links, or screenshots here if applicable.

• Upgrade poetry to 1.8.2 to fix package version conflicts with pip-tools in requirements-dev.txt
• Add docs on setting to WORKSPACE env var to be able to run tests locally
• Fix faulty type: ignore and handle type narrowing explicitly
• Add test case for high priority + zipartifact codepath for test coverage

Test Plan and Usage Guide

How did you validate that your PR works correctly? How do you run or demo the code? Provide enough detail so a reviewer can reasonably reproduce the testing procedure. Paste example command line invocations if applicable.
Tested pip install + mypy + pytest on a fresh venv using python 3.8.10

# new venv
python -m venv venvs/llm-engine
source ./venvs/llm-engine/bin/activate

# install packages
pip install -r ../requirements-dev.txt
pip install -r requirements.txt && \
    pip install -r requirements-test.txt && \
    pip install -r requirements_override.txt && \
    pip install -e .

# typecheck
mypy . --install-types

# unit tests
pytest

[seanshi-scale]

lgtm if integration tests pass, looks like some code coverage tests failed? guess we'll need to fix that too

[dmchoiboi]

Add this fixture to test the high_priority code path