New package: python3-poetry-core-1.0.3

[kwshi]

• New package: python3-poetry-core
• Manual.md: add instructions for Poetry-built Python packages

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me

[kwshi]

Resolves #30551

[kwshi]

@eli-schwartz has pointed out on #30551 that python3-pep517 packages are currently using pip, which may exhibit undesirable behavior. Currently, in this PR I've configured the package (python3-poetry-core) to build itself using PEP517, but should I switch to making it use the sdist setup.py from the PyPI tarball instead?

[eli-schwartz]

Using the setup.py has consistent semantics in line with all other python ecosystem packages and additionally reduces the bootstrap graph a bit (maybe a lot, if void were to properly devendor pip/setuptools to use system dependencies).

And the pep517 build style is not commonly used -- in fact my understanding is it was added as a precautionary measure in case it became impossible to continue maintaining existing packages without it.

[kwshi]

Alright! I have rewritten the template to build using python3-module instead of python3-pep517 now.

[kwshi]

Since it looks like poetry-core might be pushing a new release soon, and there's a decent chance (fingers crossed!) it'll include tests in its sdist (see python-poetry/poetry-core#173), perhaps we'll wait a couple days & I can update this to the newest release before merging! :)