Replace Tins::Timestamp with std::chrono::time_point

[insomniacslk]

See https://stackoverflow.com/questions/31409036/converting-from-struct-timespec-to-stdchrono/31414376 for conversion.

Verify if std::chrono::steady_clock::time_point can be used .

Basically:

timespec ts = {3, 123};  // 3 seconds + 123 nanoseconds
auto d = std::chrono::seconds{ts.seconds}
       + std::chrono::nanoseconds{ts.nanoseconds};
std::chrono::system_clock::time_point tp{d};