docs(fetch): add modern Promise.allSettled solution to fetch-users task

[illia-m-b]

Closes #3986

Description

Appends a production-grade alternative solution to the "Fetch users from GitHub" task.

Changes Made

• Appended an "Alternative modern approach" section to solution.md.
• Added a code snippet utilizing Promise.allSettled, async callbacks, and object destructuring.

Technical Rationale

The original solution intentionally mixes .then() with await for educational purposes. This addition complements the lesson by demonstrating current industry best practices:

• Pure async/await syntax without chained Promise methods.
• Graceful fault tolerance for network failures via Promise.allSettled.
• Independent, non-blocking fetch execution.