[FEA] Potential optimization: Batched memset.

[nvdbaranec]

Under some situations in the Parquet reader (particularly the case with tables containing many columns or deeply nested column) we burn a decent amount of time doing cudaMemset() operations on output buffers. A good amount of this overhead seems to stem from the fact that we're simply launching many tiny kernels. It might be useful to have a batched/multi memset kernel that takes a list of address/sizes/values as a single input and does all the work under a single kernel launch. Similar to the Cub multi-buffer memcpy or contiguous_split.