Test free-threaded Python with pytest-run-parallel

[cclauss]

To be confident about free-threaded compatibility, it is recommended to test with pytest-run-parallel.

• https://py-free-threading.github.io/testing

Something like:
% uvx --with=pytest-run-parallel pytest --iterations=8 --parallel-threads=auto

[ngoldbaum]

Passing --iterations like this makes the tests for everyone run at least 8 times slower.

Rather than editing the global tox config, I'd rather see one test job set up to run with --parallel-threads=auto and not use --iterations.

I'd rather see more attention being paid to writing multithreaded tests that use a shared Compressor and Decompressor. Maybe take a look at google/brotli#1386 for inspiration.

By the way, for all this free-threaded support stuff, I'm very happy to do all the work rather than reviewing it. You'll just have to be a little more patient with me.

[ngoldbaum]

I'm going to abort the test run here because it's still going after 1 hour.