Store jsonbin sidecar paths relative to JSON output file location

[oleksandr-pavlyk]

Closes #404

Keep --jsonbin sidecar files written next to the JSON output file, but record their filenames relative to the JSON file directory. This makes generated JSON and its sidecar directories relocatable as a unit and avoids embedding the benchmark process working-directory relationship into the JSON payload.

Add a focused json_printer test that verifies sample-time and sample-frequency sidecars are written beside the JSON file while summary filename fields contain JSON-relative paths.

[oleksandr-pavlyk]

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes

  • Improved JSON “sidecar” binary output to use more reliable, JSON-relative paths.
  • Ensure the output directory exists before writing and handle write failures more gracefully (including omitting filename/size when a sidecar can’t be produced).

• Tests

  • Expanded JSON-printer test coverage to confirm generated filename metadata is correct and referenced .bin files exist.
  • Added a failure-case test to verify correct summary omission and a single warning log when output cannot be written.

Walkthrough

The PR separates binary sidecar write paths from JSON-relative filename metadata, updates both sidecar-producing branches to use the shared helper, and adds tests plus build registration covering success and failure cases.

Changes

JSON-relative sidecar path handling

Layer / File(s)	Summary
Path helpers and directory checks nvbench/json_printer.cu	Adds std::system_error usage and helper types/functions to derive sidecar write paths and JSON-relative summary paths, then create or validate the target output directory with non-throwing filesystem error handling.
Sidecar writer and json_printer integration nvbench/json_printer.cu	Introduces a shared helper that writes JSON binary sidecars, removes partial files on failure, and populates summary metadata from the JSON-relative path; sample_times and sample_freqs now call that helper.
Test coverage and build registration testing/CMakeLists.txt, testing/json_printer.cu	Adds a dedicated nvbench test source, filesystem test scaffolding, a success case that checks JSON-relative filenames and file existence, and a failure case that checks metadata omission and warning logging.

Assessment against linked issues

Objective	Addressed	Explanation
Store sidecar filenames relative to the JSON file path in JSON output [#404]	✅
Keep writing sidecar files next to the JSON output file [#404]	✅
Validate the behavior with tests [#404]	✅

No out-of-scope changes found.

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[oleksandr-pavlyk]

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Actionable comments posted: 1

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📥 Commits

Reviewing files that changed from the base of the PR and between d483a5b and 93e5512.

📒 Files selected for processing (3)

• nvbench/json_printer.cu
• testing/CMakeLists.txt
• testing/json_printer.cu

[oleksandr-pavlyk]

The work was motivated by failure to ingest JSON file and sidecar binary files when using #386 while JSON files were generated by running CCCL benchmarks from devcontainer.

Commands used to reproduce

./bin/cub.bench.bitonic_sort.warp_keys.base -d 1 --cold-warmup-runs 16 --min-samples 100 --stopping-criterion entropy --min-r2 0.88 --jsonbin ../../../perf_data/warp-bitonic-sort-run1.json
./bin/cub.bench.bitonic_sort.warp_keys.base -d 1 --cold-warmup-runs 16 --min-samples 100 --stopping-criterion entropy --min-r2 0.88 --jsonbin ../../../perf_data/warp-bitonic-sort-run2.json

PYTHONPATH=./_deps/nvbench-src/python/scripts python ./_deps/nvbench-src/python/scripts/nvbench_compare.py ../../../perf_data/warp-bitonic-sort-run1.json ../../../perf_data/warp-bitonic-sort-run2.json