Arm backend: Preserve duplicate output slots with TOSA identity fanout

[AdrianLundell]

When FuseEqualPlaceholdersPass fuses equal constant placeholders, the graph output can contain the same node in multiple output slots. In this case ToTosaMemoryFormatPass was rewriting the output node with replace_input_with() while inserting output transposes.

That rewrote all matching occurrences at once, so duplicated logical output slots were collapsed onto the same transpose node instead of remaining distinct.

Fix this by handling duplicate outputs in the output rewrite path. For shared output nodes, create a single boundary TOSA TRANSPOSE and preserve distinct output slots by inserting TOSA IDENTITY fanout nodes for later duplicates.

This keeps insert_input_transpose() focused on normal input rewrites, avoids duplicating equivalent transposes for shared outputs, and preserves the output slot structure expected by later lowering and serialization stages.

Add regression coverage for FuseEqualPlaceholdersPass + ToTosaMemoryFormatPass with duplicate outputs, and add TOSA IDENTITY dialect and visitor coverage.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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[zingo]

Hi @digantdesai this adds file, maybe you want to check this?