feat(provider): 新增 keep_priority_on_conversion 字段，支持格式转换时保持调度优先级

tests/unit/test_provider_request_keep_priority.py

@@ -0,0 +1,14 @@
+from src.models.admin_requests import CreateProviderRequest, UpdateProviderRequest
+
+
+def test_create_provider_request_accepts_keep_priority_on_conversion() -> None:
+    req = CreateProviderRequest.model_validate(
+        {"name": "Provider Keep Priority", "keep_priority_on_conversion": True}
+    )
+    assert req.keep_priority_on_conversion is True
+
+
+def test_update_provider_request_preserves_keep_priority_on_conversion() -> None:
+    req = UpdateProviderRequest.model_validate({"keep_priority_on_conversion": True})
+    data = req.model_dump(exclude_unset=True)
+    assert data["keep_priority_on_conversion"] is True