[FEA] `sc.tl.ingest`

[maarten-devries]

Is your feature request related to a problem? Please describe.
I wish I could use rapids-singlecell to map labels and embeddings from reference data to new data

Describe the solution you'd like
Using GPU to speed up sc.tl.ingest

Is there a CPU based implementation
https://scanpy.readthedocs.io/en/stable/generated/scanpy.tl.ingest.html

[Intron7]

@maarten-devries I would have to look into the algorithm and code more closely to see if a port is possible. The Trees that ingest uses might be an issue. But I'll have a closer look into it.

[maarten-devries]

Not a high priority, more of a nice to have. Happy to help have a look at this whenever I have some time.
Thanks for the great package, by the way.