Fix timestamp parsing in python 3.10+

[Spferical]

Python 3.9 gives a deprecation warning:

$ python -c 'import datetime; import decimal; print(datetime.datetime.utcfromtimestamp(decimal.Decimal(3)))'
<string>:1: DeprecationWarning: an integer is required (got type decimal.Decimal).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
1970-01-01 00:00:03

And in python 3.10, decimal timestamp support was removed:

$ python -c 'import datetime; import decimal; print(datetime.datetime.utcfromtimestamp(decimal.Decimal(3)))'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: 'decimal.Decimal' object cannot be interpreted as an integer

[kastonework]

Thanks for this update! We'd like to take this opportunity to add some unit tests, and we plan to look at this in the next couple of weeks.