test/test_not_before_queue: Fix memory leak by freeing ineligible items in destructor

test/test_not_before_queue: Fix memory leak by freeing ineligible items in destructor

Fix memory leak in test_not_before_queue identified by AddressSanitizer.
Previously, the test was terminating without properly dequeueing all elements,
causing resource leaks during teardown.

This change implements a proper cleanup mechanism that:
1. Advances the queue's time until all elements become eligible for processing
2. Dequeues all remaining elements to ensure proper destruction
3. Guarantees clean teardown even for elements with future timestamps

The fix eliminates ASan-reported leaks occurring in the not_before_queue_t::enqueue
method when test cases were torn down prematurely.

A sample of the error from ASan:

```
Direct leak of 1800 byte(s) in 15 object(s) allocated from:
    #0 0x7f71b1f1ab5b in operator new(unsigned long) ../../../../src/libsanitizer/asan/asan_new_delete.cpp:86
    #1 0x55fb4c977058 in void not_before_queue_t<tv_t, test_time_t>::enqueue<tv_t const&>(tv_t const&) /home/kefu/dev/ceph/src/common/not_before_queue.h:164
    #2 0x55fb4c97748b in NotBeforeTest::load_test_data(std::vector<tv_t, std::allocator<tv_t> > const&) /home/kefu/dev/ceph/src/test/test_not_before_queue.cc:67
    #3 0x55fb4c961112 in NotBeforeTest_RemoveIfByClass_no_cond_Test::TestBody() /home/kefu/dev/ceph/src/test/test_not_before_queue.cc:213
    #4 0x55fb4ca05f67 in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2653
    #5 0x55fb4ca1c4f7 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2689
    #6 0x55fb4c9e1104 in testing::Test::Run() /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2728
    #7 0x55fb4c9e16e2 in testing::TestInfo::Run() /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2874
    #8 0x55fb4c9e73b4 in testing::TestSuite::Run() /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:3052
    #9 0x55fb4c9f059b in testing::internal::UnitTestImpl::RunAllTests() /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:6004
    #10 0x55fb4ca064ff in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2653
    #11 0x55fb4ca1d1bf in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:2689
    #12 0x55fb4c9e124d in testing::UnitTest::Run() /home/kefu/dev/ceph/src/googletest/googletest/src/gtest.cc:5583
    #13 0x55fb4c97a0b6 in RUN_ALL_TESTS() /home/kefu/dev/ceph/src/googletest/googletest/include/gtest/gtest.h:2334
    #14 0x55fb4c979ffc in main /home/kefu/dev/ceph/src/googletest/googlemock/src/gmock_main.cc:71
    #15 0x7f71ae833ca7 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

SUMMARY: AddressSanitizer: 1800 byte(s) leaked in 15 allocation(s).
```

Signed-off-by: Kefu Chai <tchaikov@gmail.com>