[BUG] Experiment run fails due to json parse error

### 📋 CheckList

- [x] I have searched existing issues to avoid duplicates
- [x] I am using a recently maintained version of Coze Loop
- [x] I have provided all required information
- [x] I understand this is a bug report and not a feature request
- [x] I have submitted this report in English (otherwise it will not be processed)

### 🐛 Bug Description

it produces a json parse error....

WARNING 2025-07-29 10:07:59,842 evaluator_source_prompt_impl.go:325 d8c371e4-90c8-435f-acde-1d23ceee6c47 [RunEvaluator] parseOutput Content RepairJSON fail, origin content: ```json
{
"reason": "The answer provides a detailed list of 10 of Lu Xun's works, including publication years, cover images, and brief descriptions for each. It uses precise language and offers specific information, demonstrating a thorough understanding of the topic and attention to detail.",
"score": 1
}
```, err: unexpected character: '`' at position 2
WARNING 2025-07-29 10:07:59,843 evaluator_source_prompt_impl.go:146 d8c371e4-90c8-435f-acde-1d23ceee6c47 [RunEvaluator] parseOutput fail, err: code=601205015 message=invalid output from model

### 🔄 Steps to Reproduce

1. create Evaluation set
2.create evaluators
3.create experiments

### ✅ Expected Behavior

experiments normal and get a score

### ❌ Actual Behavior

experiments runs fails

### 🚨 Severity

None

### 🔧 Component

None

### 💻 Environment

_No response_

### 🔧 Go Environment

_No response_

### 📋 Logs

```shell

```

### 📝 Additional Context

_No response_