fix: support experimental support for Deepseek models and update docs about configuration

[Hoder-zyf]

Description

When running qlib, fix the following issues based on error messages:

1. When generating hypothesis doesn't return a string, add supplementary prompt
2. DeepSeek's JSON format errors:
   a. Returns True/False, fix Python-style boolean values to JSON standard format
   b. Output code uses python xxx format, add similar parsing logic
   c. Returns multiple blocks, like json xxx python, parse the first one by default
3. Provide DeepSeek's example configuration, only need to provide DeepSeek and SiliconFlow's API keys

Motivation and Context

How Has This Been Tested?

• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Your own tests:

Types of changes

• Fix bugs
• Add new feature
• Update documentation

---

📚 Documentation preview 📚: https://RDAgent--1024.org.readthedocs.build/en/1024/