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.

readme.plan.md

@@ -4,9 +4,9 @@
 
 This plan addresses critical performance issues in SmartProxy that impact scalability, responsiveness, and stability. The approach is phased, starting with critical event loop blockers and progressing to long-term architectural improvements.
 
-## Phase 1: Critical Issues (Week 1)
+## Phase 1: Critical Issues (Week 1) ✅ COMPLETE
 
-### 1.1 Eliminate Busy Wait Loop
+### 1.1 Eliminate Busy Wait Loop ✅
 
 **Issue**: `ts/proxies/nftables-proxy/nftables-proxy.ts:235-238` blocks the entire event loop
 
@@ -31,7 +31,7 @@ await delay(retryDelayMs);
 2. Replace all synchronous sleeps with async delay
 3. Ensure all calling functions are async
 
-### 1.2 Async Filesystem Operations
+### 1.2 Async Filesystem Operations ✅
 
 **Issue**: Multiple synchronous filesystem operations blocking the event loop