Executor for polars logical plans

[wence-]

Description

This builds out the infrastructure for executing polars logical plans using pylibcudf. See docs/overview.md in the cudf_polars subdirectory for some installation guidance.

Deliberately not fully fleshing out packaging and so forth yet.

Test coverage is incomplete but growing. I'd like to get this in so other people can build on top of it.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.

[wence-]

/ok to test

[vyasr]

@wence- once you merge in the latest 24.06 I'm happy to take a pass at reviewing. It's fine if you want to keep in draft and you don't think it's quite ready for full review yet, but I figured I'd take a pass once you're reasonably happy so that we can iron out as many issues as possible immediately.

[wence-]

Took a pass through the tests. I don't have much to say on them content-wise, they all look fine to me and it seems like you have good coverage. Organization-wise, though, I'm confused at what went into test_basic.py and what got its own module. Can we establish some sort of organizational principle from the get-go?

No good reason for this split (other than test_basic was written earlier), will split them out appropriately.

[wence-]

/merge