Add Compressedbackend for Onebit optimizers (#5473)
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
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Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
