Add Promise/Async API Support

[r-el]

Summary

This PR adds full Promise-based API support alongside the existing callback-based methods.

Changes

New Features

• Promise API: All CRUD methods now have async counterparts (createAsync, readAllAsync, etc.)
• Async/Await Support: Modern async/await syntax support
• TypeScript Integration: Updated type definitions for Promise methods

Implementation

• Added async-wrapper.js utility for converting callback methods to Promises
• Updated main class to include async methods in constructor
• Created comprehensive test suite for async operations
• Added async usage example (async-demo.js)

Documentation

• Updated README with Promise API documentation
• Added async/await usage examples
• Updated feature list to include Promise support

Testing

• All existing tests pass
• New async test suite with 10 comprehensive tests
• All examples work correctly

Breaking Changes

None - this is fully backward compatible.

Examples

// New async API
const user = await db.createAsync({ name: 'John', age: 30 });
const users = await db.readAllAsync();
await db.updateAsync(user.id, { age: 31 });
await db.deleteAsync(user.id);

// Original callback API still works
db.create({ name: 'Jane' }, (err, user) => {
  // callback implementation
});

Commits

• Add async wrapper utilities for JsonFileCRUD with Promise-based API
• Add async method variants to JsonFileCRUD for improved usability
• Add callback-based methods to JsonFileCRUD interface for improved functionality
• Add async demo example to showcase Promise-based API usage
• Add async tests for JsonFileCRUD methods to validate functionality
• Add async/await usage examples to README for enhanced clarity
• Update CHANGELOG.md for version 1.3.0: Add async/await API support and enhanced examples
• Update package.json for version 1.3.0: Add async tests and examples to improve coverage and clarity
• Add Promise-based API section to README with async method examples