fix: spawn time of control units and clock init time

• the control unit spawn time was initialized only when the control unit was stepped for the first time but the spawn time is needed for HasFinished(), which is called by the OSC1 engine before the control units are stepped for the first time (see here and here). Therefore initializing the spawn time with the current clock time upon instantiation in i_abstract_control_unit.h for all control units
• furthermore, the clock was initialized with start time 40ms. Although this is reset to 0ms in the SimulatorImpl constructor, this is annoying for unit tests, where no SimulatorImpl class is instantiated. Fixed that.
• since the clock is not reset from the test framework between different test cases of one test suite (singleton which is not destroyed) and this can lead to side effects, introduced manual reset of clock.h in SetUp() of every control unit test case (with common test class)