Move dev requirements to pyproject.toml

[EwoutH]

Removes requirements-dev.txt file and consolidates those requirements as optional dependencies in pyproject.toml with the [dev] extra.

Also requires a newer version of Cython for Python 3.11, and specify minimum instead of specific versions for Cython and Descartes.

[jorisvandenbossche]

FYI we might temporarily move away again from having the project details in pyproject.toml because it is still experimental in setuptools (and not supported everywhere, such as debian), see #1533. So I would keep this on hold until we made a decision there.

[coveralls]

Pull Request Test Coverage Report for Build 3217818103

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.582%

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Totals
Change from base Build 3217626353:	0.0%
Covered Lines:	2145
Relevant Lines:	2536

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💛 - Coveralls

[EwoutH]

In June they removed the experimental status for a lot of parts of the pyproject.toml configuration, including project metadata (see current docs).

It is been a few months since the implementation of PEP 621 support landed in setuptools (after a long period of feedback), and it seems now that support for project metadata in pyproject.toml has stabilised. Moreover the existing implementation is backed by a PEP, therefore it makes sense to consider this part of the feature stable.

[mwtoews]

Apologies @EwoutH as I've prepared a similar #1606