Add managed_gradient_accumulation for ZeRO stage 0/1 (#8184)
When managed_gradient_accumulation=false, disable micro-step tracking
and treat each engine.step() as the accumulation boundary: reduce
locally accumulated grads then apply the optimizer update. Stage 2/3 and
pipeline remain unsupported in this change.
Part fix for #8183
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Signed-off-by: Olatunji Ruwase <tunji.ruwase@snowflake.com>
Co-authored-by: Cursor <cursoragent@cursor.com>
