Minimal padding in pool allocator

[awnawab]

Currently, to protect from misaligned addresses on device, every allocation is padded to 8 bytes in the pool allocator. This would mitigate a lot of the device memory bandwidth benefits from running in single precision. A potential fix could be to only pad those allocations that are not multiples of nproma, as these are for all intents and purposes guaranteed to be multiples of 8.