Use pyproject.toml to install build dependencies.

[SamWilsn]

For whatever reason, installing using pip within pip doesn't work in pypy. Presumably because of something to do with build isolation. This commit adds a pyproject.toml with the required packages, so that the dependencies are installed before entering setup.py.

[megtog]

Saw this comment at #1596 (comment)

pyproject.toml

Agree it's neat, but hesitant to introduce extra files into global scope of the specs repo. It's really just the regular setuptools setup, with some extra distutils commands. No exotic build system to reference.

maybe outdated maybe relevant 😀

[SamWilsn]

Unfortunately there is an exotic build system; it just happens to fit entirely in setup.py 🤣

[megtog]

My knowledge of Python packaging is quite limited. However, I would like to share my experience.

It seems with this pyprojet.toml change, one can import eth2spec at root directory (no need to cd ./tests/core/pyspec anymore, I saw people struggle with this when starting hacking on consensus-specs before)