Add tau-bench client rollout support

[bradhilton]

Summary

• Add an art.tau_bench client and rollout helper for tau-bench scenarios.
• Add bounded retries for transient gateway statuses and transport errors while preserving a stable request ID across attempts.
• Update Tinker dependencies used by the caladan tau-bench experiment.

Test plan

• uv run pytest tests/unit/test_tau_bench_client.py
• uv run ruff check src/art/tau_bench tests/unit/test_tau_bench_client.py
• Supervised uv run experiments/044-art-tau-bench.py -s agent-20m-test2 for 20 minutes without tau-bench client/server exceptions.