Legalize large-stride non-overlapping maxpool on U55

[apullin]

Summary: Teach the Arm partitioner to recognize exact U55 large-stride non-overlapping max-pool operations as safely decomposable, without mutating the graph during partitioning. Backend preprocessing then canonicalizes value-only max_pool2d_with_indices and rewrites eligible pools into supported stride-1 reductions. This preserves the partitioner contract, keeps unrelated TOSA/VGF/U85 paths unchanged, and also covers exported MaxPool1d.

Differential Revision: D113087299

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