Add performance optimization reference guide and runnable examples

[Copilot]

Provides a comprehensive resource for identifying and optimizing inefficient code patterns across JavaScript and Python.

Content Structure

• PERFORMANCE_GUIDE.md: 8 optimization categories with before/after examples

  • Algorithm complexity (O(n²) → O(n))
  • Memory management, caching, concurrency
  • Database, network, and string operations

• Runnable benchmarks: examples/performance_examples.{js,py}

  • Demonstrates 10x to 1000x+ improvements
  • Results stored to prevent compiler optimization

• Benchmark utilities: examples/benchmark_utils.js

  • Function comparison and memory profiling tools

Example Optimization

// Inefficient: O(n²) nested loops
function findCommon(arr1, arr2) {
  const common = [];
  for (let i = 0; i < arr1.length; i++) {
    for (let j = 0; j < arr2.length; j++) {
      if (arr1[i] === arr2[j]) common.push(arr1[i]);
    }
  }
  return common;
}

// Optimized: O(n) using Set
function findCommon(arr1, arr2) {
  const set2 = new Set(arr2);
  return arr1.filter(item => set2.has(item));
}

Benchmarks show 100x+ improvement for 1000+ element arrays.

Original prompt

Identify and suggest improvements to slow or inefficient code

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