Run tests on CI with cargo-nextest

[messense]

trafficstars

https://github.com/nextest-rs/nextest

Try it out to see if it can help speeding up CI runs.

[messense]

test marker::tests::test_acquire_gil ... FAILED

https://github.com/PyO3/pyo3/blob/b8dd626194cc97ad878adc7b45d6098e760ac05a/src/marker.rs#L993-L1010

This one seems problematic with cargo-nextest.

https://nexte.st/book/how-it-works.html

[birkenfeld]

Last time I checked, nextest did not support and run doctests. So you'd have to add "cargo test --doc" as a separate step?

[messense]

Last time I checked, nextest did not support and run doctests. So you'd have to add "cargo test --doc" as a separate step?

In that case I think we should wait for https://github.com/nextest-rs/nextest/issues/16, otherwise the added cargo test --doc steps might just slow things down and make the CI setup more complex.