Fix connection leak in route-connection-handler by using safe socket creation

The previous fix only addressed ForwardingHandler classes but missed the critical setupDirectConnection() method in route-connection-handler.ts where SmartProxy actually handles connections. This caused active connections to rise indefinitely on ECONNREFUSED errors.

Changes:
- Import createSocketWithErrorHandler in route-connection-handler.ts
- Replace net.connect() with createSocketWithErrorHandler() in setupDirectConnection()
- Properly clean up connection records when server connection fails
- Add connectionFailed flag to prevent setup of failed connections

This ensures connection records are cleaned up immediately when backend connections fail, preventing memory leaks.

readme.hints.md

@@ -457,4 +457,11 @@ const socket = createSocketWithErrorHandler({
 - `test/test.forwarding-error-fix.node.ts` - Tests forwarding handlers handle errors gracefully
 
 ### Configuration
-No configuration changes needed. The fix is transparent to users.
+No configuration changes needed. The fix is transparent to users.
+
+### Important Note
+The fix was applied in two places:
+1. **ForwardingHandler classes** (`https-passthrough-handler.ts`, etc.) - These are standalone forwarding utilities
+2. **SmartProxy route-connection-handler** (`route-connection-handler.ts`) - This is where the actual SmartProxy connection handling happens
+
+The critical fix for SmartProxy was in `setupDirectConnection()` method in route-connection-handler.ts, which now uses `createSocketWithErrorHandler()` to properly handle connection failures and clean up connection records.