Migrate Python dependency uiri/toml to tomllib / hukkin/tomli

[Contextualist]

Reasons for the migration:

1. hukkin/tomli has been accepted as part of the Python standard library (see PEP680 and bpo-40059: tomllib python/cpython#31498), named as tomllib, and will be released along with Python 3.11.
2. uiri/toml is unmaintained since Oct 2020, while hukkin/tomli is an actively maintained implementation of TOML 1.0 spec, with 100% test coverage.

[netlify]

✔️ Deploy Preview for maturin-guide canceled.

🔨 Explore the source changes: b896ade

🔍 Inspect the deploy log: https://app.netlify.com/sites/maturin-guide/deploys/621af41e90f94b0007c3cfab

[messense]

I remember setuptools-rust removed tomli dependency due to a issue from cryptography: pyca/cryptography#6671 (comment) , I'm not sure if it also affects building maturin from sdist if we merge this.

[Contextualist]

If I understand correctly, this is referring to the circular dependency problem between flit and tomli.

flit depends on tomli starting from version 3.4, while they fixed the circular dependency issue in version 3.6 by vendoring tomli.

Building tomli>=1.1.0 from sdist requires flit_core>=3.2.0,<4, so those who have to use flit_core version 3.4, 3.5, or 3.5.1 will probably experience the issue.

[messense]

Thanks for the clarification!

Building tomli>=1.1.0 from sdist requires flit_core>=3.2.0,<4, so those who have to use flit_core version 3.4, 3.5, or 3.5.1 will probably experience the issue.

I think this is fine now since flit_core is already fixed in recent versions.