Handle missing phase service token

[nimish-ks]

~/git/phase/python-sdk main* 20s ❯ python main.py         
Traceback (most recent call last):
  File "/phase/python-sdk/main.py", line 5, in <module>
    phase = Phase(
            ^^^^^^
  File "/phase/python-sdk/src/phase/phase.py", line 84, in __init__
    self._phase_io = PhaseIO(init=init, pss=pss, host=host)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/phase/python-sdk/src/phase/utils/phase_io.py", line 53, in __init__
    self.is_service_token = pss_service_pattern.match(app_secret) is not None
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^