Static keyword arguments forwarded to init_chat_model.
Once a profile is constructed, its kwargs can be read but not
rewritten — for example, profile.init_kwargs["temperature"] = 2.0
raises TypeError. The registry stores its own defensive copy, so
mutating the dict you passed into the constructor after the fact won't
affect the registered profile either. To change a registered profile's
kwargs, re-register (which merges on top) or construct a new profile.
When both init_kwargs and init_kwargs_factory are set on the same
profile, the factory's output overrides init_kwargs on key collision.
