[DO NOT MERGE] 2.9, Inductor partition, standalone compile, monkeypatch fix(es)

[ProExpertProg]

In-progress PR to test 2.9 in CI with inductor partitioning and standalone compile.

Includes:

• 2.9 changes from @huydhn: Update PyTorch to 2.9.0+cu129 #24994
• turning on inductor partitioning by default
• reenabling standalone compile

Fixes in main:

• [BugFix] Work around graph partition x torch.compile cache issue #26956 AOT caching issue fix
• [BugFix] Patch inductor partitioning logic #26735 monkeypatch
• [BugFix] Patch inductor memory plan logic #26878 monkeypatch for memory plan output naming
• [Graph Partition] pass tests for decorator #26831 decorator tests
• [torch.compile] Fix tests for torch==2.9 inductor partition #26116 piecewise test fixes
• disable graph partition in custom op #26952 fix for nested compilation (to replace fused_moe::grouped_topk fix)
• [torch.compile] fix simple inductor graph partition test #27050 fix simple inductor partition test

Past fixes no longer necessary:

• disabling nested compilation on fused_moe::grouped_topk - superseeded by disable graph partition in custom op #26952
• forcing spawn (both tests and vllm MP) to circumvent cuda init issue
  • Likely a temporary transformers issue, fixed
  • see [DO NOT MERGE] 2.9, Inductor partition, standalone compile, monkeypatch fix(es), spawn #26882 with spawn.

[ProExpertProg]

@BoyuanFeng LORA test failure seems relevant: perhaps we need to review how we deal with weak_ref_tensors with inductor partitioning but also not sure why there's a CPU tensor there.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @ProExpertProg.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @ProExpertProg.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork