trunk/abaacefd1437dd1e192a2b10a110654c69443e08: Enable nested reductions by default in OSS (#191974)

发生了什么

This change was prepared with AI assistance and reviewed by the author. Enable nested reductions by default in OSS now that the staged reduction support has landed. Use the standard Config/JustKnob integration while retaining TORCHINDUCTOR_NESTED_REDUCTION as the force override. Internal enablement is gated by JustKnob and will be rolled out incrementally. Also does a few long tail fixes: Tests that encoded the unfu…

摘要按规则整理自下方来源原文

来源