fix: add safe destroy check for proxy agents in terminate method

Proxy agents like tunnel-agent and hpagent may not implement the standard
destroy() method, causing TypeError when the interceptor attempts cleanup.
Added proper type checking before calling agent.destroy() to prevent crashes
with CONNECT tunneling requests.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: luisAzcuaga

src/interceptors/ClientRequest/NodeClientRequest.ts

@@ -609,7 +609,9 @@ export class NodeClientRequest extends ClientRequest {
      * debatable, but we should still handle this case gracefully.
      * @see https://github.com/mswjs/interceptors/issues/304
      */
-    // @ts-ignore
-    this.agent?.destroy()
+    const agent = (this as any).agent
+    if (agent && typeof agent.destroy === 'function') {
+      agent.destroy()
+    }
   }
 }