Fix ZeRO parameter alignment for grouped_mm (#8277)
## Summary
ZeRO stage 1/2 stores model parameters as views into flattened fp16/bf16
buffers. Individual parameter views can start at non-16-byte offsets
even when the flat buffer itself is aligned, which breaks
alignment-sensitive kernels such as `torch._grouped_mm`.
Pad parameter boundaries inside the ZeRO flat buffer so model parameter
views remain 16-byte aligned without duplicating misaligned parameters.
The padded layout is propagated through partition/gradient offsets,
LP↔HP linkage, DeepCompile gradient buffers, checkpoint restore, and
`zero_to_fp32` reconstruction.
Older checkpoints without parameter-alignment padding remain loadable;
their compact layout is converted when restored.
## Tests
- ZeRO-1/2 BF16 regression with a deliberately misaligned parameter
layout.
- Verifies zero-copy aligned flat-buffer views across optimizer steps.
- Verifies checkpoint reload with `load_module_only=True` and
`load_optimizer_states=False`.
- Synced with current `master`, including the ZeRO-1/2 DeepCompile file
rename.
Fixes #8276
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Signed-off-by: Cao Yuhang <caoyuhang@fwerkor.com>
Signed-off-by: Masahiro Tanaka <tanaka.masahiro@gmail.com>
Co-authored-by: Masahiro Tanaka <tanaka.masahiro@gmail.com>
Co-authored-by: Masahiro Tanaka <81312776+tohtana@users.noreply.github.com>
