local_microsec_clock::local_time(time_zone_ptr) occasionally returns an incorrect time

Extremely rarely, a call to `local_microsec_clock::local_time(time_zone_ptr)` will return a result about 1 second in the past.

On my local machine, running the following code:
```c++
#include
#include

int main() {
boost::local_time::time_zone_ptr zone(new boost::local_time::posix_time_zone("EST-5"));

for (int i = 0; i < 100'000'000; ++i)
{
boost::local_time::local_date_time t0 = boost::local_time::local_microsec_clock::local_time(zone);
boost::local_time::local_date_time t1 = boost::local_time::local_microsec_clock::local_time(zone);
if (t1 < t0)
{
std::cout << i << ": time went from " << t0 << " to " << t1 << '\n';
}
}

return 0;
}
```
produces ~10-15 incorrect results for 100M calls, or one incorrect result per ~7-10M calls.

The output suggests that this always occurs when the second ticks. The fractional part rolls over, but the seconds do not change.
```
81899680: time went from 2023-Aug-21 09:17:12.999739 EST to 2023-Aug-21 09:17:12.000740 EST
91444271: time went from 2023-Aug-21 09:17:27.999755 EST to 2023-Aug-21 09:17:27.000752 EST
92719444: time went from 2023-Aug-21 09:17:29.999467 EST to 2023-Aug-21 09:17:29.000465 EST
```

It looks like the issue is caused by the second ticking between the calls to `second_clock::universal_time()` and `second_clock::local_time()`, which causes `utc_offset` to be off by 1 second.
https://github.com/boostorg/date_time/blob/39714907b7d32ed8f005b5a01d1c2b885b5717b3/include/boost/date_time/microsec_time_clock.hpp#L59-L66

I intend to submit a PR with a solution soon.