docs: clarify and update requirements of the async-race task

[zagorky]

Title of Pull Request

🤔 This is a ...

• 🌟 New task
• 🌐 New module
• ⚙️ Update to an existing task
• 🔧 Update to an existing module
• 🔗 Update or addition of external resources or links
• 🐛 Fix in a task or related content
• 🛠 Fix in a module or related content
• ✏️ Fixed a typo or grammatical error
• 🔗 Fixed a broken link
• ❓ Other (specify: ****____****)

Description

• Brief Overview:

Update requirements due to Airbnb style guide incompatibility, clarify allowed CSS libraries, and restrict type assertions.

• Implementation Approach:

1. Replace Airbnb style guide with Unicorn style guide;
2. Define allowed CSS libraries;
3. Restrict type assertions and non-nullable type assertions;

Additional Information

• Screenshots/Links:
• Related Issues:

Checklist

• ✅ I have performed a self-review of my own code.
• 📝 I have commented my code, particularly in hard-to-understand areas.
• 🔧 I have made corresponding changes to the documentation (if applicable).
• 🚫 My changes generate no new warnings or errors.

[stardustmeg]

Please, run prettier for us to have consistent formatting in the school materials 🤗