fix: make model_info optional in ShowResponse for cloud models

[Pawansingh3889]

Fixes #607.

Problem

Some cloud models (e.g. glm-4.7:cloud, qwen3-next:80b-cloud, deepseek-v3.2:cloud) return /api/show responses that omit the model_info field entirely. The ShowResponse Pydantic model has model_info typed as Optional but uses Field(alias=...) without a default value, which makes Pydantic treat it as required:

Fix

One-line change in _types.py:

Adding default=None makes Pydantic respect the Optional type hint when the field is missing from the API response.

Testing

Verified both cases:

• Response without model_info (cloud models): parses successfully, modelinfo is None
• Response with model_info (standard models): parses successfully, modelinfo contains the data

[Pawansingh3889]

Hi, this is a one-line fix for issue #607 — cloud models that omit model_info cause a ValidationError. Tested both cases (with and without model_info). Let me know if any changes are needed.