[meta] UMAP fixes for 25.04

[jcrist]

Opening a meta issue for centralizing PRs and issues we want resolved before the 25.04 release (across all rapids repos). Please feel free to add new PRs/issues to the list as things come up.

cuml

• Correct UMAP dispatch trigger condition #6330
• UMAP fixes #6316
• Use L2Expanded/L2SqrtExpanded instead of the *Unexpanded variants #6303
• Plumb metric and metric_kwds through to UMAP with nn_descent #6304
• Reduce peak memory in UMAP.fit/UMAP.fit_transform #6323

raft

• Swap blocks and threads_per_block in compute_graph_laplacian raft#2597
• Fix COO symmetrization raft#2582
• Fix duplicate indices in batch NN Descent raft#2586

[jcrist]

(assigning myself just as the person tracking to ensure all these get in and we're in a good state pre-25.04 release, not as the person who should be doing all the work here :)).