Update translation prompt

[LoserCheems]

This pull request updates the translation guidelines in src/small_thoughts/utils/prompt.py to improve clarity and consistency for both English-to-Chinese and Chinese-to-English translations. The changes include adding new rules for handling markup and code snippets, as well as refining existing instructions.

Updates to translation guidelines:

• Added rules to retain original markup symbols (e.g., <tool>, </tool>) and to only translate comments and descriptive text within code snippets, leaving the code itself untranslated.
• Adjusted the Chinese-to-English translation system prompt to specify that ambiguity in the original text should be preserved in the translation when applicable.
• Refined the guideline for translating technical or specialized vocabulary to ensure accurate translation without necessarily including the original term in parentheses.