Fix poetry show package dir

[blast-hardcheese]

How poetry calculates the env path has changed, so instead of trying to guess, just delegate to poetry env. If the environment hasn't been created we don't get a path, which is only relevant if we're in a completely blank environment, so it's hopefully not that bad.

• Renaming Python3Backend to PythonPoetryBackend
• Rely on poetry env list to find the active environment
• General housekeeping

[blast-hardcheese]

A question from @airportyh around how to test this seems to have been eaten by GitHub, but the following is an example:

upm (nix) ((f547cb7...)) dstewart$ cd /tmp/poetry-test
poetry-test (nix) dstewart$ ~/Projects/upm/cmd/upm/upm show-package-dir
--> poetry env list --full-path
poetry-test (nix) dstewart$ ~/Projects/upm/cmd/upm/upm add requests
--> poetry add requests
Creating virtualenv poetry-test-cX6xfNfC-py3.10 in /Users/dstewart/Library/Caches/pypoetry/virtualenvs
Using version ^2.31.0 for requests

Updating dependencies
Resolving dependencies... (0.2s)

Package operations: 5 installs, 0 updates, 0 removals

  • Installing certifi (2023.11.17)
  • Installing charset-normalizer (3.3.2)
  • Installing idna (3.6)
  • Installing urllib3 (2.1.0)
  • Installing requests (2.31.0)

Writing lock file
poetry-test (nix) dstewart$ ~/Projects/upm/cmd/upm/upm show-package-dir
--> poetry env list --full-path
/Users/dstewart/Library/Caches/pypoetry/virtualenvs/poetry-test-cX6xfNfC-py3.10

Since we are delegating the show-package-dir subcommand directly to poetry env list, the virtualenv doesn't exist until the first time a package operation has been performed, hence the result being empty in the first invocation.

[cdmistman]

cool! thanks!