Fix editable installation for cuda-core

[leofang]

Description

Close #1088.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[kkraus14]

Tested locally and worked with both uv pip install --system -v -e . and pip install -v -e .

[leofang]

/ok to test c97f405

[rwgk]

Locally tested: I rebuilt from scratch using -e for pathfinder, bindings, core, then ran the tests.

(I glanced through the changes but don't understand them enough to meaningfully review.)

[leofang]

(I glanced through the changes but don't understand them enough to meaningfully review.)

The tl;dr is that when implementing a custom build frontend (our build_hooks.py), we are required to implement hooks from both PEP-517 and PEP-660, the latter of which are needed for editable install. I kept it as a TODO back in #1041, hoping that no one would try to do -e before I circle back to work on this. I was wrong.

[github-actions]

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