Add parquet benchmark for output_dict_columns option

[y2kiran]

Description

This PR adds benchmarks to test the newly added output_dict_columns options for the Parquet reader, which was introduced in this PR

Checklist

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

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Added a Parquet dictionary-transcoding benchmark.
  • Compares string materialization, dictionary encoding, and direct dictionary transcoding.
  • Reports timing, memory usage, throughput, file size, and direct-transcoding speedups across configurable data and I/O scenarios.

Walkthrough

Changes

Parquet dictionary benchmark

Layer / File(s)	Summary
Benchmark modes and result reporting cpp/benchmarks/io/parquet/parquet_reader_dict.cpp	Defines three read modes, dictionary-width estimation, run configuration, timing collection, and comparison output.
Fixture generation and mode execution cpp/benchmarks/io/parquet/parquet_reader_dict.cpp	Generates configurable dictionary-encoded Parquet data and runs string, dictionary-encoded, and direct-transcoding reads.
Validation, metrics, and target wiring cpp/benchmarks/io/parquet/parquet_reader_dict.cpp, cpp/benchmarks/CMakeLists.txt	Validates output types, skips plain-encoded direct-transcode cases, records performance metrics, configures benchmark axes, and adds the source to the NvBench target.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• rapidsai/cudf#22532: Introduces the same Parquet dictionary reader benchmark implementation and CMake wiring.

Suggested labels: improvement

Suggested reviewers: pointkernel, mhaseeb123, pmattione-nvidia, davidwendt, devavret

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title accurately identifies the main change as adding a Parquet benchmark, although it does not specify the reader dictionary-transcoding focus.
Description check	✅ Passed	The description directly explains that the pull request adds benchmarks for the Parquet reader's output_dict_columns options.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[vuule]

Could we add this to parquet_reader_options.cpp and follow the existing benchmark patterns there? Since this measures output_dict_columns, keeping it with the other reader-options benchmarks would make it easier to find and maintain.
Could we also make the PR title more specific, for example: “Add benchmark for Parquet output_dict_columns”?