Add concept constraint to UniqueTimestampFactory

[uselessgoddess]

add

static_assert(IFactory<UniqueTimestampFactory, Timestamp>, 
                    "/* your message */");

after this

Timestamps/cpp/Platform.Timestamps/UniqueTimestampFactory.h

Lines 3 to 13 in e2f21fd

	class UniqueTimestampFactory
	{
	private: std::uint64_t _lastTicks = 0;
	public: Timestamp Create()
	{
	auto utcTicks = common_era_clock::to_ticks(common_era_clock::now());
	_lastTicks = utcTicks > _lastTicks ? utcTicks : _lastTicks + 1;
	return Timestamp(_lastTicks);
	}
	};