Download and cache the PJRT plugins needed to run pjrt.
The CPU plugin is always installed. The CUDA plugin is installed in
addition when a CUDA-capable GPU is detected, or when cuda = TRUE is
passed explicitly.
Plugins are otherwise downloaded lazily the first time a client is
created, but the download requires user confirmation, unless
the environment variable PJRT_INSTALL=1.
Value
(character())
The platforms that were installed, invisibly.