[TRACKER] cuml.benchmark tool improvements

[dantegd]

We are incrementally improving the cuML benchmark harness so it can support declarative benchmark suites, cleaner result artifacts, better console output, stronger CPU/GPU comparisons, and cuml.accel benchmarking.

This issue tracks the benchmark-harness improvement work across the current PR stack

Tasks:

• Add YAML-based benchmark definitions for cuML regression runs Add YAML based benchmark definitions for cuML regression runs #7980
• Default CPU benchmark estimators to max parallelism Default CPU benchmark estimators to max parallelism #8025
• Improve benchmark progress output formatting Improve benchmark progress output formatting #8026
• Add JSON output for benchmark results Add JSON output for benchmark results #8027
• Add cuml.accel support as a benchmark backend