feat: implement rateLimit() utility for function call throttling

[Rasagnika-GR]

🎯 Overview

Implements a reusable rateLimit() utility that restricts how many times a function can be called within a specified time interval. This is a common production pattern used to prevent API abuse, protect rate-limited endpoints, and control resource usage.

Closes #58

🔧 Changes Made

New File: utils/rateLimit.js

• Implemented rateLimit(fn, config) using a counter + timestamp window approach
• Resets call count automatically after the interval expires (lazy reset — no persistent timers)
• Preserves function context and arguments via fn.apply(this, args)
• Exported as a named ES6 export

Edge Cases Handled

• Non-function input → throws TypeError
• Missing or invalid config object → throws TypeError
• limit <= 0 → throws RangeError
• interval <= 0 → throws RangeError
• Rapid consecutive calls exceeding limit → throws Error('Rate limit exceeded')

🧪 Testing

const limitedFn = rateLimit(apiCall, { limit: 3, interval: 1000 });

// Within limit — all resolve normally
limitedFn(); // ✅ allowed
limitedFn(); // ✅ allowed
limitedFn(); // ✅ allowed
limitedFn(); // ❌ throws Error('Rate limit exceeded')

// After 1000ms interval resets — allowed again
setTimeout(() => limitedFn(), 1000); // ✅ allowed

// Edge cases
rateLimit('not-a-function', { limit: 3, interval: 1000 }); // TypeError
rateLimit(apiCall, null);                                   // TypeError
rateLimit(apiCall, { limit: 0, interval: 1000 });          // RangeError
rateLimit(apiCall, { limit: 3, interval: -1 });            // RangeError