[benchmark_app] Keep every averaged profiling counter without mutating requests

[zorox06]

Details

The average JSON report keeps only the first layer because each averaged node is passed as a separate request and only request zero is serialized. Both JSON and CSV averaging also modify the original ProfilingInfo objects. Share an aggregator that builds new counters, then serialize every averaged layer as one request.

Tests cover Two-layer JSON and CSV averages, totals, metadata, unchanged source timings, repeatable report generation, an empty request and reordered layers.

Validation

• 3 regression tests passed against this branch.
• Windows, Python 3.12.14, OpenVINO 2026.4.1 runtime wheel, NumPy 2.4.2.
• git diff --check passed.

Run the regression tests with the matching OpenVINO runtime installed:

PYTHONPATH=tools/benchmark_tool python -m pytest tools/benchmark_tool/unit_tests/test_average_counters.py -q

AI Assistance

AI assistance used: yes, for implementation and regression testing.