bump NCCL floor to 2.19

[jameslamb]

Follow-up to #2443

As part of the work to support NumPy 2 across RAPIDS, we found reason to upgrade some libraries like cugraph to slightly newer NCCL (>=2.19). Context: rapidsai/build-planning#102 (comment)

This applies that same bump here, to keep the range of NCCL versions consistent across RAPIDS.

[jakirkham]

Thanks James! 🙏

[jakirkham]

One build failed with a networking error. Will wait for the rest of the builds to complete and then restart

[jameslamb]

@jakirkham I just cancelled CI and restarted the failed jobs.

conda-cpp-build is upstream of a lot of other jobs, including conda-cpp-tests which can take 2-3 hours to run 😬

I know we're getting very close to code freeze... will leave it to @cjnolet 's discretion whether to admin-merge at some point or to wait for all those test jobs to run. I think we can be highly confident that this will work, given that the tests were all already using NCCL 2.22 on this previous successful run: https://github.com/rapidsai/raft/actions/runs/11040960166/job/30673327293

(and should continue to, given that this just moves the floor from >=2.18 to >=2.19)

[jakirkham]

Sounds good. Thanks James! 🙏

Have also mentioned this PR in the release thread offline. So it is being tracked there

[cjnolet]

/merge

[jakirkham]

Thanks James and Corey! 🙏