fix: close all proxy connections before closing server in test afterAll

In undici v8, ProxyAgent defaults proxyTunnel to true, which means
CONNECT tunneling is used even for HTTP-to-HTTP proxy requests.
These tunnel connections keep the proxy server alive, preventing
proxyServer.close() from completing within the 10s afterAll timeout.

Adding proxyServer.closeAllConnections() before proxyServer.close()
forcefully terminates the tunnel connections and allows cleanup.

Agent-Logs-Url: https://github.com/node-modules/urllib/sessions/4c3edcc4-7c2f-4451-b8f8-b324a333958d

Co-authored-by: fengmk2 <156269+fengmk2@users.noreply.github.com>

Author: Copilot

test/options.dispatcher.test.ts

@@ -27,6 +27,7 @@ describe('options.dispatcher.test.ts', () => {
 
   afterAll(async () => {
     await close();
+    proxyServer.closeAllConnections();
     await new Promise((resolve) => {
       proxyServer.close(resolve);
     });