Add a converter for datetime.datetime <--> Timestamp.

[mjohanse-emr]

What does this Pull Request accomplish?

Adds a DateTimeConverter class that converts python datetime.datetime objects to protobuf timestamp_pb2.Timestamp objects. I put this converter in builtin.py since we do not own either type. They are included as built-in types for python/protobuf.

timestamp_pb2.Timestamp has ToDatetime and FromDatetime functions which make this conversion easy.

Once we add converters for hightime.datetime and/or bintime.DateTime, we'll have to update the python type checking logic to differentiate between these three different "datetime" types. I'm not including any of that logic in this PR.

Why should this Pull Request be merged?

Implements part of AB#3166769

What testing has been done?

Unit tests, mypy, pyright, styleguide

I ran the all_types example and this is what shows up for datetime:

[github-actions]

Test Results

   10 files  ± 0     10 suites  ±0   21s ⏱️ ±0s
  224 tests + 3    224 ✅ + 3  0 💤 ±0  0 ❌ ±0 
2 190 runs  +30  2 190 ✅ +30  0 💤 ±0  0 ❌ ±0 

Results for commit 1f08864. ± Comparison against base commit 2e9b3ba.

This pull request removes 29 and adds 32 tests. Note that renamed tests count towards both.

tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object10-Collection.bool]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object11-Collection.bytes]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object12-Collection.float]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object13-Collection.int]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object14-Collection.str]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object15-Collection.bool]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object16-Collection.bytes]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object17-Collection.float]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object18-Collection.int]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object19-Collection.str]
…

tests.unit.test_convert ‑ test___python_datetime_datetime___to_any___valid_timestamppb2_value
tests.unit.test_convert ‑ test___timestamppb2_timestamp___from_any___valid_python_value
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object10-datetime]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object11-Collection.bool]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object12-Collection.bytes]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object13-Collection.float]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object14-Collection.int]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object15-Collection.str]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object16-Collection.bool]
tests.unit.test_convert ‑ test___various_python_objects___get_best_matching_type___returns_correct_type_string[python_object17-Collection.bytes]
…

♻️ This comment has been updated with latest results.