Enable auto-rebuild in scikit-build-core at import time

[horizon-blue]

Closes MET-41

Summary of Changes

scikit-build-core has an editable.rebuild option, which can automatically invoke CMake under the hood when we import from genmetaballs to rebuild the C++ extension if needed. To use this option, we need to turn off build isolation for our package so that scikit build can use the right set of tools (see scikit-build/scikit-build-core#1112 (comment)). On the other hand, this also makes rebuilding a lot faster because Pixi doesn't have to re-create a new isolated environment and build from scratch.

See scikit-build-core's official doc on editable install for more details.

With this change, we shouldn't need to manually run pixi reinstall genmetaballs anymore. Hopefully this will make our development experience a bit smoother :).

Test Plan

After enabling this option & run pixi reinstall genmetaballs one last time just to make sure that the config is active. Then, I tried modifying a couple of the C++ files, then run pixi run test immediately after (without running reinstall manually), and the changes are correctly reflected on the Python test results.

[linear]

MET-41 Speed up pre-push behavior

Right now, pushing is very slow because it unconditionally does a pixi reinstall genmetaballs before running the tests during pre-push (see MET-28). This takes over 40s on my side every-time I need to push.

A smarter way would be to conditionally re-install only when the build files are not updated to any source code. This could be automated via some script.

---

scikit-build-core has an editable.rebuild option, which can automatically rebuild the package at import time if needed (see the official doc for details). This can save us from having to explicitly invoking pixi reinstall genmetaballs.

[horizon-blue]

I'm going to merge this now so we can develop faster. Lmk if it breaks your workflow, and we can always revert this setting if needed :)