fix(providers): defer builtin provider instantiation to fix gunicorn startup crash

[fancyboi999]

Problem

gunicorn 启动时 worker 进程直接崩溃，报 pydantic ValidationError: Input should be a valid dictionary or instance of ModelInfo。uvicorn 不受影响。

Root Cause

provider_manager.py 在模块顶层创建了 ~80 个 ModelInfo pydantic 实例和 ~20 个 Provider 实例。

当用户用 PYTHONPATH=src/ 配合 gunicorn 启动时，同一个 .py 文件可以通过两条路径被 Python 加载——一次走 PYTHONPATH，一次走 site-packages。Python 把它们当成两个不同模块，分别创建了两个 ModelInfo 类。

MODELSCOPE_MODELS 的元素用的是 class-A 的 ModelInfo，但 OpenAIProvider 的 pydantic schema 绑的是 class-B。pydantic v2 做 isinstance() 检查时发现不匹配，直接抛 ValidationError。

本地复现脚本：

# 两个同名但不同身份的 ModelInfo 类
ns_a, ns_b = {}, {}
exec("from pydantic import BaseModel\nclass ModelInfo(BaseModel): id: str", ns_a)
exec("from pydantic import BaseModel\nclass ModelInfo(BaseModel): id: str", ns_b)

instance = ns_a['ModelInfo'](id='test')
isinstance(instance, ns_b['ModelInfo'])  # False — 触发 ValidationError

Fix

两处改动：

1. 模型数据改成 plain dict — dict 没有类身份，pydantic 在验证时会用当前进程里的 ModelInfo 来构造，不存在 A/B 不匹配
2. Provider 实例化从模块级常量移到 _create_builtin_providers() 工厂函数 — 在 ProviderManager.__init__() 时才调用，此时所有 import 已完成，类身份稳定

Validation

# 单元测试
pytest tests/unit/ → 518 passed

# gunicorn 真实启动 (2 workers)
gunicorn qwenpaw.app._app:app --worker-class uvicorn.workers.UvicornWorker --workers 2
→ [INFO] Booting worker with pid: 87119
→ [INFO] Booting worker with pid: 87120
→ [INFO] Application startup complete.  (×2)
→ 零 ValidationError，零 worker 崩溃

Closes #3375

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[Copilot]

Pull request overview

This PR addresses a gunicorn multi-worker startup crash caused by Pydantic v2 class-identity mismatches when modules are imported via multiple paths. It does so by avoiding module-import-time creation of Pydantic ModelInfo/Provider instances and deferring built-in provider instantiation until ProviderManager initialization.

Changes:

• Replace built-in model definitions from List[ModelInfo] to plain List[dict] to avoid cross-module isinstance() mismatches.
• Move built-in provider instantiation from module-level constants to a lazy _create_builtin_providers() factory invoked by ProviderManager._init_builtins().
• Update unit tests to validate built-in providers via _create_builtin_providers() / updated model definitions.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/qwenpaw/providers/provider_manager.py	Defers built-in provider instantiation and switches model definitions to plain dicts to prevent gunicorn/Pydantic import-identity crashes.
tests/unit/providers/test_siliconflow_provider.py	Adjusts tests to locate SiliconFlow providers via the new factory instead of removed module-level constants.
tests/unit/providers/test_opencode_provider.py	Adjusts tests to locate OpenCode provider via the new factory instead of removed module-level constants.
tests/unit/providers/test_kimi_provider.py	Adjusts tests for new Kimi model data structure (dicts) and provider factory usage.

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