Fix flakiness in QuicEventLoop unit tests

This also changes the logic of EpollServer-based event loop to handle timeouts
correctly.

PiperOrigin-RevId: 466038831

quiche/quic/core/io/quic_all_event_loops_test.cc

diff --git a/quiche/quic/core/io/quic_all_event_loops_test.cc b/quiche/quic/core/io/quic_all_event_loops_test.cc
index f2a3cfe..16eb344 100644
--- a/quiche/quic/core/io/quic_all_event_loops_test.cc
+++ b/quiche/quic/core/io/quic_all_event_loops_test.cc
@@ -411,7 +411,7 @@
 }
 
 TEST_P(QuicEventLoopFactoryTest, NegativeTimeout) {
-  constexpr auto kAlarmTimeout = QuicTime::Delta::FromMilliseconds(500);
+  constexpr auto kAlarmTimeout = QuicTime::Delta::FromSeconds(300);
   auto [alarm1_ptr, delegate1] = CreateAlarm();
 
   alarm1_ptr->Set(clock_.Now() + kAlarmTimeout);