Convert naive/local datetimes to UTC in TestResult and Step serialization

[Copilot]

TestResult and Step reject naive datetimes at serialization time because hightime_datetime_to_protobuf requires UTC. Users providing datetime.now() get a cryptic ValueError: The tzinfo must be datetime.timezone.utc.

Changes

• _grpc_conversion.py — Added _ensure_utc() helper that calls astimezone(timezone.utc), which correctly handles both naive datetimes (treated as local time) and tz-aware datetimes
• _test_result.py, _step.py — Import and apply _ensure_utc() in to_protobuf() before passing datetimes to hightime_datetime_to_protobuf()

Example

# Previously raised: ValueError: The tzinfo must be datetime.timezone.utc.
test_result = TestResult(
    name="name",
    start_date_time=datetime.now(),   # naive local time — now accepted
    end_date_time=datetime.now(),
    outcome=Outcome.PASSED,
)
client.create_test_result(test_result)  # internally converts to UTC

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create result requires that I provide uct time</issue_title>
<issue_description>Trying to call create_test_result with the following code will throw an error that the start and end times have to be in utc. The python API should allow me to provide local time and internally convert to utc.

test_result = TestResult(
        name="name",
        start_date_time=datetime.now(),
        end_date_time=datetime.now(),
        outcome=Outcome.PASSED,
    )

AB#3746793</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create result requires that I provide uct time #110

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[csjall]

@copilot Ideally we should update the hightime_datetime_to_protobuf method in protobuf library to ensure UTC. This way each and every Python client which uses hightime_datetime_to_protobuf should not need to implement _ensure_utc.

[Copilot]

That's a good long-term suggestion. However, ni-protobuf-types is a separate externally-published package (ni.protobuf.types v1.1.0) installed as a dependency — it lives in its own repository and would require its own release cycle to update. Since we can't change it from here, keeping _ensure_utc() in this library is the right approach. If the upstream fix is desired, it should be tracked as a separate issue/PR in the ni-protobuf-types repository.