text: Title: Replace type_workarounds.NotImplementedType
  Body: **Description of the issue**
  
  Python 3.10 (our minimum requirement) provides [types.NotImplementedType](https://docs.python.org/3.10/library/types.html?highlight=notimplementedtype#types.NotImplementedType).  The following workaround is redundant and can be replaced with that type -
  https://github.com/quantumlib/Cirq/blob/351a08e52b7090cfab3a1ad07859ebf09d54052a/cirq-core/cirq/type_workarounds.py#L15-L23
  
  **TODO**
  
  - switch to types.NotImplementedType in the code
  - delete the type_workarounds module
  
  **Cirq version**
  
  1.5.0.dev at 351a08e52b7090cfab3a1ad07859ebf09d54052a.