Fix freezegun related issues (#3399)
Fix freezegun related issues (#3399)

- Freezegun assumes that naive timestamps are UTC and changes
timestamps under the hood.  For example,
   datetime.datetime.fromtimestamp(52).timestamp() may not equal 52.0

We may want to get rid of freezegun since it is starting to be more
trouble than it is worth, but that's a problem for another day.
quantumlib/Cirq,balopat/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,quantumlib/Cirq,balopat/Cirq