Introduction of the raft::device_resources_snmg type

[viclafargue]

Introduces the raft::device_resources_snmg type to hold all resources required for the NCCL clique.

Answers #2459
Removed call to raft::comms::build_comms_nccl_only (#2465)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.16%. Comparing base (d7e68f5) to head (9780ca5).

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-25.02    #2487   +/-   ##
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  Coverage         81.16%   81.16%           
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  Files                19       19           
  Lines               515      515           
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  Hits                418      418           
  Misses               97       97           

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[cjnolet]

Took another look and I think the implementation itself is great. The only suggestions I have are related to the docs. I understand this is a lower-level detail for most users but we should strive to provide as much info and details as possible for both end-users AND for future implementors of SNMG algorithms.