Add comprehensive middleware execution order and error handling examples

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PR: Comprehensive Middleware Guide and Deep Dive Examples

#Overview This PR introduces a detailed Middleware Guide and corresponding interactive examples for Express.js. It provides developers with a deeper understanding of middleware execution order, error handling, async patterns, and best practices, addressing gaps in existing documentation.

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New Files Created

1.examples/middleware-deep-dive/index.js`** – Interactive example demonstrating:

• Correct middleware execution order
• Async error handling
• Side-by-side comparisons of correct vs incorrect patterns
• Console output to visualize middleware flow

This PR enhances Express.js documentation by providing a comprehensive middleware guide with interactive examples, covering execution order, error handling, and async patterns. It directly addresses developer pain points and improves learning resources.

Fixes: #6923