fix: ensure python poetry envs are created when installing

[agdimech]

• use pnpm instead of yarn for non-node projects.
• force usage of pyenv as a global dependency as this leads to more predicatable installs/builds and less errors to do with python aliases, etc
• Ensure all non-node projects have their install:ci target called as part of the root install:ci script
• Ensure all python projects call poetry env use pythonXXX before installing to ensure the venv is setup correctly.
  • The logic here is to parse the pyproject.toml and fetch the listed python version. If it starts with a '^', we fetch the latest installed python version from the user's machine matching the major version. If the version is pinned, then we use that version.
• Update docs to mention pyenv should be used.
• Replace yarn with pnpm in getting started.

[cogwirrel]

Nice, this is going to make python a lot more robust :)