This symbol is a type alias.
cirq.Duration or value that can trivially converted to one.
DURATION_LIKE = Union[ NoneType, datetime.timedelta, ForwardRef('cirq.Duration') ]
datetime.timedelta is a
cirq.DURATION_LIKE. It is converted while
preserving its duration.
None is a
cirq.DURATION_LIKE that converts into a zero-length duration.
Note that 0 is a
DURATION_LIKE, despite the fact that
int is not listed,
because 0 is the only integer where the physical unit doesn't matter.