Skip redundant run_decompositions when no ops match decomp table

[apullin]

Summary:
Adds an early-exit check to _gen_edge_manager_for_partitioners: before
calling program.run_decompositions(table), scan the graph for ops that
appear in the decomposition table. If none are found, skip the call
entirely.

Each run_decompositions call performs a full re-export of the program
via make_fx(), re-tracing every node through FakeTensor dispatch.
On the EDGE_DO_NOT_DECOMP path this function is called up to 3 times;
the early-exit eliminates at least one redundant call where the previous
pass already decomposed all matching ops.

The check recursively walks control flow submodules (cond/map/scan) to
avoid incorrectly skipping when decomposable ops are nested.

Benchmark

Model: small CNN feature extractor (~50K params, 9 conv layers with
LayerNorm, targeting Ethos-U55 via the ARM/TOSA lowering pipeline).
Graph: ~1200 nodes.

lower() before: 82 s
lower() after: 71 s
Delta: -11 s (-13 %)

Differential Revision: D96489903

[pytorch-bot]

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❌ 5 Awaiting Approval, 1 New Failure, 2 Unrelated Failures

As of commit 4f1a818 with merge base 59838fc ():

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• Build Cadence (gh)
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NEW FAILURE - The following job has failed:

• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 7b18441cf82c4cb76e28291c00b85b3627bd57edfcab4978fe970b22ce9c9795 /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[meta-codesync]

@apullin has exported this pull request. If you are a Meta employee, you can view the originating Diff in D96489903.

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