feat(performance): Add async utility functions and filesystem utilities

- Implemented async utilities including delay, retryWithBackoff, withTimeout, parallelLimit, debounceAsync, AsyncMutex, and CircuitBreaker.
- Created tests for async utilities to ensure functionality and reliability.
- Developed AsyncFileSystem class with methods for file and directory operations, including ensureDir, readFile, writeFile, remove, and more.
- Added tests for filesystem utilities to validate file operations and error handling.

test/core/utils/test.async-utils.ts

@@ -0,0 +1,200 @@
+import { tap, expect } from '@git.zone/tstest/tapbundle';
+import { 
+  delay, 
+  retryWithBackoff, 
+  withTimeout, 
+  parallelLimit,
+  debounceAsync,
+  AsyncMutex,
+  CircuitBreaker
+} from '../../../ts/core/utils/async-utils.js';
+
+tap.test('delay should pause execution for specified milliseconds', async () => {
+  const startTime = Date.now();
+  await delay(100);
+  const elapsed = Date.now() - startTime;
+  
+  // Allow some tolerance for timing
+  expect(elapsed).toBeGreaterThan(90);
+  expect(elapsed).toBeLessThan(150);
+});
+
+tap.test('retryWithBackoff should retry failed operations', async () => {
+  let attempts = 0;
+  const operation = async () => {
+    attempts++;
+    if (attempts < 3) {
+      throw new Error('Test error');
+    }
+    return 'success';
+  };
+  
+  const result = await retryWithBackoff(operation, {
+    maxAttempts: 3,
+    initialDelay: 10
+  });
+  
+  expect(result).toEqual('success');
+  expect(attempts).toEqual(3);
+});
+
+tap.test('retryWithBackoff should throw after max attempts', async () => {
+  let attempts = 0;
+  const operation = async () => {
+    attempts++;
+    throw new Error('Always fails');
+  };
+  
+  let error: Error | null = null;
+  try {
+    await retryWithBackoff(operation, {
+      maxAttempts: 2,
+      initialDelay: 10
+    });
+  } catch (e: any) {
+    error = e;
+  }
+  
+  expect(error).not.toBeNull();
+  expect(error?.message).toEqual('Always fails');
+  expect(attempts).toEqual(2);
+});
+
+tap.test('withTimeout should complete operations within timeout', async () => {
+  const operation = async () => {
+    await delay(50);
+    return 'completed';
+  };
+  
+  const result = await withTimeout(operation, 100);
+  expect(result).toEqual('completed');
+});
+
+tap.test('withTimeout should throw on timeout', async () => {
+  const operation = async () => {
+    await delay(200);
+    return 'never happens';
+  };
+  
+  let error: Error | null = null;
+  try {
+    await withTimeout(operation, 50);
+  } catch (e: any) {
+    error = e;
+  }
+  
+  expect(error).not.toBeNull();
+  expect(error?.message).toContain('timed out');
+});
+
+tap.test('parallelLimit should respect concurrency limit', async () => {
+  let concurrent = 0;
+  let maxConcurrent = 0;
+  
+  const items = [1, 2, 3, 4, 5, 6];
+  const operation = async (item: number) => {
+    concurrent++;
+    maxConcurrent = Math.max(maxConcurrent, concurrent);
+    await delay(50);
+    concurrent--;
+    return item * 2;
+  };
+  
+  const results = await parallelLimit(items, operation, 2);
+  
+  expect(results).toEqual([2, 4, 6, 8, 10, 12]);
+  expect(maxConcurrent).toBeLessThan(3);
+  expect(maxConcurrent).toBeGreaterThan(0);
+});
+
+tap.test('debounceAsync should debounce function calls', async () => {
+  let callCount = 0;
+  const fn = async (value: string) => {
+    callCount++;
+    return value;
+  };
+  
+  const debounced = debounceAsync(fn, 50);
+  
+  // Make multiple calls quickly
+  debounced('a');
+  debounced('b');
+  debounced('c');
+  const result = await debounced('d');
+  
+  // Wait a bit to ensure no more calls
+  await delay(100);
+  
+  expect(result).toEqual('d');
+  expect(callCount).toEqual(1); // Only the last call should execute
+});
+
+tap.test('AsyncMutex should ensure exclusive access', async () => {
+  const mutex = new AsyncMutex();
+  const results: number[] = [];
+  
+  const operation = async (value: number) => {
+    await mutex.runExclusive(async () => {
+      results.push(value);
+      await delay(10);
+      results.push(value * 10);
+    });
+  };
+  
+  // Run operations concurrently
+  await Promise.all([
+    operation(1),
+    operation(2),
+    operation(3)
+  ]);
+  
+  // Results should show sequential execution
+  expect(results).toEqual([1, 10, 2, 20, 3, 30]);
+});
+
+tap.test('CircuitBreaker should open after failures', async () => {
+  const breaker = new CircuitBreaker({
+    failureThreshold: 2,
+    resetTimeout: 100
+  });
+  
+  let attempt = 0;
+  const failingOperation = async () => {
+    attempt++;
+    throw new Error('Test failure');
+  };
+  
+  // First two failures
+  for (let i = 0; i < 2; i++) {
+    try {
+      await breaker.execute(failingOperation);
+    } catch (e) {
+      // Expected
+    }
+  }
+  
+  expect(breaker.isOpen()).toBeTrue();
+  
+  // Next attempt should fail immediately
+  let error: Error | null = null;
+  try {
+    await breaker.execute(failingOperation);
+  } catch (e: any) {
+    error = e;
+  }
+  
+  expect(error?.message).toEqual('Circuit breaker is open');
+  expect(attempt).toEqual(2); // Operation not called when circuit is open
+  
+  // Wait for reset timeout
+  await delay(150);
+  
+  // Circuit should be half-open now, allowing one attempt
+  const successOperation = async () => 'success';
+  const result = await breaker.execute(successOperation);
+  
+  expect(result).toEqual('success');
+  expect(breaker.getState()).toEqual('closed');
+});
+
+tap.start();