chore: benchmark routing + tool-call validation

[saschabuehrle]

Summary

• unify benchmark model overrides + provider/cost resolution
• enrich benchmark routing metrics + add real-world tool-call benchmark
• fix full benchmark dataset handling and baseline cost calculations
• add mmlu benchmark concurrency and fix bfcl parallel tool-call evaluation

Testing

• python3 -m pytest
• benchmarks: longbench_full, gsm8k_full, mmlu_full, mtbench_full, bfcl_full, ruler_full, truthfulqa, tool_calls(+agentic/realworld), bfcl agentic, basic_usage (py/ts)