Change initialization style from copy initialization to direct initialization (which is more permissive) in `AgentReduce` to allow a wider range of types to be used with it.
Change initialization style from copy initialization to direct initialization
(which is more permissive) in `AgentReduce` to allow a wider range of types to
be used with it.

NVlabs/CUB,NVIDIA/cub,NVlabs/cub