`ZeusProfilingService` for profiling energy with NVML energy query method on arbitrary profile windows

[Rosie-m]

In response to #12, this PR uses nvmlDeviceGetTotalEnergyConsumption for GPU architectures Volta and later.

Main Changes and Benefits

• We created a new class ZeusProfilingWindow. It profiles energy and time profiling on arbitrary windows inside training scripts. Meanwhile, multiple profile windows are stored in a FIFO stack, which allows simultaneous profiling at different levels during the training.
• We integrated ZeusProfilingService into ZeusDataLoader. This abstracted away the logic of computing time and energy consumption.
• ZeusProfilingService will decide the energy query method in a per-GPU manner. nvmlDeviceGetTotalEnergyConsumption will be used for GPUs architectures Volta and later; power polling with Zeus Monitor will be used for GPUs with older architectures.

[jaywonchung]

@Rosie-m The changes look all good! Thanks a lot.

I pushed some small changes. Can you take a look?