Build/Release testing

[teald]

Summary

This tests astrodata against built and "published" packages using devpi as a PyPI mirror. This is a major step towards ensuring issues like Issue #28 are caught, which often pass in local testing.

Major changes

• Add build test support with a dedicated PyPI mirror
  • Can run locally or via github actions
  • devpi is only additional dependency
• Update development docs for nox usage
• Add nox sessions for creating venvs and conda envs with dependencies installed

nox -s devshell  # Create a development .venv
nox -s devconda  # Create a development conda env

Other changes

• Update the formatting and linting workflows to consolidate settings into the pyproject.toml
  • Previously, these were a bit scattered (some set in .pre-commit-config.yaml, others set in pyproject.toml or in environment variables/global settings.

Notes

• Given the general use cases for spinning up isolated, temporary devpi servers in isolated environments, that component will likely be extracted into some kind of nox plugin or utility.