[cudf] Thread memory resources through equality/hash row preprocessing

[nirandaperera]

Description

Depends on #23581

A part of #20780.

Equality and hash preprocessed_table paths still allocated temps from the current device resource, so harness-based tests could not prove explicit MR routing. This change requires cudf::memory_resources on those APIs and updates callers accordingly.

• Equality/hash preprocessed_table::create, self_comparator, two_table_comparator, and row_hasher take required mr and use mr.get_temporary_mr() for preprocessing temps
• Call sites across join/groupby/hash/search/reductions/etc. pass an explicit mr
• Add BaseFixtureWithHarness and convert row-operator tests to use harness stream()/resources(), with TODOs where lexicographic still falls back to the current resource

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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