feat(perf): Add performance measuring api

[TatianaFomina]

Performance Monitoring API

This PR adds a new Performance Monitoring API to track application performance metrics.

Features

• Track transactions and spans with timing data
• Automatic span completion when transaction ends
• Support for both browser and Node.js environments
• Debug mode for development
• Graceful cleanup on page unload/process exit

API

// Start a transaction
const transaction = hawk.startTransaction('page-load', {
  page: '/home',
  type: 'navigation'
});

// Create spans within transaction
const span = hawk.startSpan(transaction.id, 'api-call', {
  url: '/api/users'
});

// Finish span when operation completes
span.finish();

// Finish transaction
transaction.finish();