Fix memory leaks and crashes in ETCP tests

✅ Fixed critical segmentation fault (SIGABRT) in test_etcp_two_instances
✅ Added comprehensive timer debug logging with DEBUG_CATEGORY_TIMERS
✅ Created uasync_print_resources() function for resource diagnostics
✅ Created utun_instance_diagnose_leaks() function for leak analysis
✅ Fixed cleanup order - cancel timers before destroying uasync instances
✅ Fixed timer cancellation to properly update counters
✅ Fixed socket cleanup to unregister from uasync before destruction
✅ Added detailed diagnostic output for memory leak tracking
✅ All tests now pass without crashes

Key fixes:
- Fixed use-after-free in test cleanup sequence
- Added proper timer leak detection and cleanup
- Enhanced debug capabilities for future debugging
- Fixed ETCP socket cleanup to prevent resource leaks

The test_etcp_two_instances now runs successfully without segmentation faults.

lib/debug_config.h

@@ -38,6 +38,7 @@ typedef enum {
     DEBUG_CATEGORY_CONFIG      = 1 << 7,   // configuration parsing
     DEBUG_CATEGORY_TUN         = 1 << 8,   // TUN interface
     DEBUG_CATEGORY_ROUTING     = 1 << 9,   // routing table
+    DEBUG_CATEGORY_TIMERS      = 1 << 10,  // timer management
     DEBUG_CATEGORY_ALL         = 0xFFFFFFFF
 } debug_category_t;