Add Compressedbackend for Onebit optimizers

[Liangliang-Ma]

In the process of adding onebit optimizers support for XPU devices, we have noticed that for different accelerator, the main difference of implementation of compressed_allreduce lies on packbits and unpackbits. CUDA uses cupy and NPU uses torch_npu. Instead of replace these to xpu only functions, we provided a CompressedBackend to do the compressed_allreduce work where users can add their own packbits/unpackbits kernels, which is a general path for all kinds of accelerators.

In this PR, we:

1. Add CompressedBackend for onebitAdam, onebitLamb and zerooneAdam
2. Add XPU implement of packbits/unpackbits with SYCL, built in PackbitsBuilder
3. Add tests for onebit with CompressedBackend

[delock]

@Liangliang-Ma the function documentation needs to be moved to line 39 right before the function def line.

[Liangliang-Ma]

Updated.

[delock]

@tjruwase this PR is an approach to abstract the generic part of 1bit-adam and implment accelerator dependent part with DeepSpeed custom op builder. So 1bit-adam does not need to depend on accelerator specific libraries.

@inkcherry I remember you investigated in 1bit adam portability before, FYI this PR implement a portable version of 1bit adam support.

[Liangliang-Ma]

Hi @tjruwase , could you please help to review this PR? Thanks!

[Liangliang-Ma]

@tjruwase I have noticed that in onebit unit test, the onebit comm backend is assigned like this:
"comm_backend_name": get_accelerator().communication_backend_name().
But in fact, it's not the same thing, for get_accelerator().communication_backend_name() chooses which backend to do regular comm, like broadcast, allgather etc, while onebit backend specifies how to do error-compensated compression. We have MPI-based onebit backend not in accelerators' comm backend. And also I found that both HPU and NPU accelerator have 'hccl' communication_backend_name, which will lead to same onebit backend. So maybe we can change this part? How about we add a interface under accelerator like get_accelerator().onebit_backend() or change unit test to a more general way? Thanks.

[Liangliang-Ma]

@tjruwase Hi, May I ask if you could help to review my last comment or merge this one first? Thanks

[tjruwase]

@Liangliang-Ma, apologies for delay. I am still thinking about your last comment, but will not delay this PR.