Enforcing DocDetails.tzinfo to be UTC

[jamesbraza]

Seen in client code:

Traceback (most recent call last):
  ...
    result = sum(doc_details_to_combine)
  File "/layers/google.python.pip/pip/lib/python3.13/site-packages/paperqa/types.py", line 1058, in __add__
    PREFER_OTHER = self.publication_date <= other.publication_date
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: can't compare offset-naive and offset-aware datetimes

This PR resolves this issue by ensuring all publication_date are in UTC

[Copilot]

Pull Request Overview

This PR resolves a TypeError that occurs when comparing offset-naive and offset-aware datetimes by enforcing all DocDetails.publication_date fields to be in UTC timezone.

• Added a field validator to DocDetails class that ensures all publication dates are converted to UTC
• Updated test data to use UTC-aware datetime objects
• Added UTC import to necessary files

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/paperqa/types.py	Added field validator to convert publication_date to UTC and imported UTC
tests/test_clients.py	Updated test datetime objects to use UTC timezone and imported UTC

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[dosubot]

Related Documentation

Checked 1 published document(s). No updates required.

^{How did I do? Any feedback?}  

[dosubot]

Documentation Updates

Checked 1 published document(s). No updates required.

^{How did I do? Any feedback?}