Move content of the Python pkg to subdirectory python/kvikio/

[hcho3]

Part of #369

[wence-]

Tiny niggle, approving python changes.

[bdice]

I think the devcontainer failures will require a change to https://github.com/rapidsai/devcontainers/blob/bff06939d44479ae1f63c3f128881d6d533de99c/features/src/rapids-build-utils/opt/rapids-build-utils/manifest.yaml#L48

This change would be similar to the changes in rapidsai/devcontainers#263 when we moved rmm's package directory from python to python/rmm.

It looks like rapidsai/devcontainers#283 does this and more?

[hcho3]

@bdice Let's merge this PR first. I would like to proceed as follows:

1. Merge this PR.
2. Submit a smaller PR to devcontainer to account for the directory change (python -> python/kvikio).
3. Merge add wheel output #369 to add libkvikio and create C++ wheels
4. Submit a separate PR to devcontainer to add libkvikio.

[bdice]

@hcho3 Sounds fine to me. You'll probably need to get admin-merges to work around the circular dependency between this PR and the one you plan to file to rapidsai/devcontainers.

[raydouglass]

Admin merging due to circular dependency