Add Poetry build backend support

[bact]

Background

Pitloom 0.5.1 cannot extract any project metadata from https://github.com/mistralai/mistral-inference (see #62) because the project uses Poetry build backend (https://python-poetry.org/ ), which is not supported yet.

Pitloom 0.5.1 supports 2 build backends: Hatchling https://hatch.pypa.io/ and setuptools https://setuptools.pypa.io/

As Poetry is also popular, need to consider adding it.

• Read [tool.poetry] in pyproject.toml for metadata
  • See https://python-poetry.org/docs/pyproject/#the-toolpoetry-section
• Read poetry.lock for metadata and dependencies
• Work with poetry-core build backend (possible hook for build-time generation?)