[Dev] Param offset in _ParamAndGradBucket should be aligned

[BestJuly]

What does this PR do ?

Migrate PR#3007 to dev branch.

Pasted the original introduction here:
param_to_index in _ParamAndGradBucket would be used when mxfp8 primary weight is set by fp8_param_gather.
The param offset should be aligned to 64 if distributed optimizer is used. Otherwise, if there are params whose numel is not 64-aligned, finish_param_sync would copy incorrect weights for mxfp8 primary weight as (param_start, param_end) are incorrect.

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[skydoorkai]

lgtm