pyproject.toml build-system should use poetry-core instead of poetry

[huantianad]

• [x] I have searched the issues of this repo and believe that this is not a duplicate.
• [x] I have searched the documentation and believe that my question is not covered.

Issue

The python packages that this project uses all use poetry's build system, and thus all have something like

[build-system]
requires = ["poetry>=0.12"]
build-backend = "poetry.masonry.api"

in their pyproject.toml files, which allows the packages to be built via a PEP517 frontend. However, we should instead depend on poetry-core instead of poetry in the build-system section, as we don't need the CLI tools of poetry to build the package, just the build system.

[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

Should be used instead.

See https://github.com/python-poetry/poetry-core#why-is-this-required for more info.

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[johan-bjareholt]

@ErikBjare Anything stopping us to just take in all these patches?

[ErikBjare]

Nope, going through them now :)

[ErikBjare]

All merged! Thanks @huantianad! ❤️