feat: support GPT-5 reasoning and verbosity controls

[endymion]

Summary

• add runtime reasoning_effort and verbosity support for GPT-5-family controls
• propagate controls through Tactus runtime, DSPy agent/configuration, ModelPrimitive, and LLM backend paths
• map verbosity for Responses mode through text.verbosity while preserving chat-mode kwargs

Verification

• GitHub Actions Release workflow passed on Python 3.10, 3.11, and 3.12
• pytest targeted runtime/helper failures pass locally
• ruff and black checks pass locally for changed tests

Release

Semantic Release-compatible change commit is included: feat: support GPT-5 reasoning and verbosity controls