chore: update versions in new project init

[henryiii]

Summary

This updates the versions a bit in the new project init. Scikit-build-core updated to 0.12+, pybind11 updated to 3+ (which allows a small simplification), and PyO3 updated to 0.28.2+ (which is what I was running into, it was on an old version).

I also wanted to update the gitignore, as it's missing a bunch of things for Maturin (like target/* and *.so!), but I guess that's somewhere else.

[konstin]

Thanks for doing these updates!

[konstin]

I'm wary of adding a ** prefix here, it would mean we have to traverse the entire tree each time, which can be a performance hazard. src/** for example is less risky as users don't generally put large trees, say caches, data to be processed or venvs, into src.

[henryiii]

I'll remove it, I feel like I've wanted to add it before but we had the same conversation, yes, don't want to traverse into venvs and such. :)

(The problem is that users often have per-directory CMakeLists.txt) src would be pretty common, but you could also have some in include, for example. (and tests, but those don't natter for rebuilds).)

[konstin]

Thanks!