Move replicated-output dedup to the Dask and Ray frontends

[Matt711]

Description

• Reverts Multi-rank fixes for cudf-polars streaming #22361, which suppressed replicated chunks at intermediate operators and broke downstream consumers under multi-rank.
• Dedupe replicated outputs once, at the Dask and Ray frontends where the client concatenates per-rank results. SPMD returns per-rank results unchanged.
• ChannelMetadata.duplicated=True now consistently means every rank holds the data.
• Depends on Run the cudf-polars test suite against DaskEngine and RayEngine #22381

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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