Introspection: add a CLI to generate stubs

[Tpt]

Useful for setuptools-rust

Use it also for the integration tests

[davidhewitt]

Thanks, the binary implementation looks fine to me (and matches what I've done locally in testing previously).

Some thoughts / questions:

• Will we ship prebuilt versions of this, e.g. on this repository? If no, will setuptools-rust build it from scratch?
• Does this affect any planned integration with maturin (e.g. make it irrelevant?)
• Should we document how to use this in type-stub.md?

[Tpt]

Will we ship prebuilt versions of this, e.g. on this repository? If no, will setuptools-rust build it from scratch?

Good question. Building in this repository and publish on pypi is likely the easiest and nicest way to go. This way setuptools-rust can just depend on it. Glad to do the basic setup if you are ok with this idea.

Does this affect any planned integration with maturin (e.g. make it irrelevant?)

No, maturin integration is imho still very relevant as an "integrated" tool doing everything (build + introspection). We just merged PyO3/maturin#3105 with first integration bit (a --generate-stubs option that adds stubs to the built artifacts).

Should we document how to use this in type-stub.md?

Definitely. Done. I have also added some documentation for the new maturin features.

[Tpt]

@davidhewitt just a small up to make sure you have seen my answers. Sorry for that

[davidhewitt]

Makes sense, I think we can indeed ship on PyPI with the same version numbering we use for the rest of PyO3?

[davidhewitt]

(That can be a follow-up, I guess)

[codspeed-hq]

Merging this PR will improve performance by 13.8%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 104 untouched benchmarks
⏩ 1 skipped benchmark¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	bench_pyclass_create	4.6 µs	4 µs	+13.8%

---

_{Comparing Tpt:tpt/introspection-bin (9583119) with main (cf4d883)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[Tpt]

Makes sense, I think we can indeed ship on PyPI with the same version numbering we use for the rest of PyO3?

@davidhewitt Done. I have written the publishing action and setup a "pending publisher" on Pypi. When the next release is done I can share the package with you.