dmagdavector

The release information on the GitHub page for 1.4.3: * https://github.com/mej/nhc/releases/tag/1.4.3 should probably be copied into the RELEASE_NOTES.txt file.

Update version of iperf3 from 3.6 to 3.16

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### Steps to reproduce Spack currently only explicitly has version 3.6 of the iPerf3 package (out of ESnet / LBNL). This makes the default the latest version of 3.16, and...

cuda: add v12.5.0

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NB: support for PowerPC has been dropped in CUDA 12.5, so "Linux-ppc64le" local installer option is no longer present.