Use cargo nextest for running our tests

[cwfitzgerald]

Connections

None

Description

This uses cargo-nextest to run our tests.

This provides a couple of benefits:

• Runs each test in its own process, preventing issues with EGL's single threadedness.
• Runs all tests individually and in parallel.

Testing

It is.

[cwfitzgerald]

See https://github.com/gfx-rs/wgpu/runs/5257083717?check_suite_focus=true for a good example of how clear this new test framework makes errors extremely clear, even if we didn't see them before.

[cwfitzgerald]

I think this is a much better experience than what we had before, for basically zero CI cost.