Slow lookup

Compared lookup + ToTm with analogs from C/C++. It turned out to be 2.5 and 8 times slower. cctz takes the last date of the time zone and [shifts it](https://github.com/google/cctz/blob/master/src/time_zone_info.cc#L870). Also, for optimization, we add [some transitions](https://github.com/google/cctz/blob/master/src/time_zone_info.cc#L597) (constantly moving them too). Strange and slow. Do you want to fix it?

Bencmark
```
BM_Time_ToCivilUTC_CCTZ 55.4 ns 55.4 ns 12012245 8.38x
BM_Time_ToCivilUTC_Libc 22.6 ns 22.6 ns 30427869 3.42x
BM_Time_ToCivilUTC_Libcpp 6.61 ns 6.87 ns 97881024 1x
```

Source code BM_Time_ToCivilUTC_Libcpp
```cpp
constexpr int get_yearday(const std::chrono::year_month_day& ymd) noexcept {
constexpr int k_month_offsets[1 + 12] = {
-1, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
};
const int feb29 = (ymd.month() > std::chrono::February && ymd.year().is_leap());
const unsigned month = static_cast(ymd.month());
return k_month_offsets[month] + feb29 + static_cast(ymd.day()) - 1;
}

std::tm TpToTm(const std::chrono::system_clock::time_point tp) {
std::chrono::sys_days days = std::chrono::floor(tp);
std::chrono::year_month_day ymd{days};
auto seconds = std::chrono::duration_cast(tp - days);
std::chrono::hh_mm_ss hms{seconds};

std::tm tm{};
tm.tm_year = static_cast(ymd.year()) - 1900;
tm.tm_mon = static_cast(ymd.month()) - 1;
tm.tm_mday = static_cast(ymd.day());
tm.tm_wday = static_cast(std::chrono::weekday{days}.c_encoding());
tm.tm_yday = get_yearday(ymd);
tm.tm_hour = hms.hours().count();
tm.tm_min = hms.minutes().count();
tm.tm_sec = hms.seconds().count();

return tm;
}

void BM_Time_ToCivilUTC_Libcpp(benchmark::State& state) {
std::chrono::system_clock::time_point tp =
std::chrono::system_clock::from_time_t(1384569027);
while (state.KeepRunning()) {
tp += std::chrono::seconds(1);

benchmark::DoNotOptimize(TpToTm(tp));
}
}
BENCHMARK(BM_Time_ToCivilUTC_Libcpp);
```