feat(api): expose last_updated for a unit

[nijel]

Proposed changes

Fixes #11786

Checklist

• [ ] Lint and unit tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added documentation to describe my feature.
• [ ] I have squashed my commits into logic units.
• [ ] I have described the changes in the commit messages.

Other information

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.57%. Comparing base (6aee586) to head (95fda7f). Report is 3906 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/WeblateOrg/weblate/pull/11839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=WeblateOrg) ```diff @@ Coverage Diff @@ ## main #11839 +/- ## ========================================== - Coverage 90.82% 90.57% -0.25% ========================================== Files 554 576 +22 Lines 57306 58703 +1397 Branches 9122 9384 +262 ========================================== + Hits 52046 53173 +1127 - Misses 3640 3831 +191 - Partials 1620 1699 +79 ``` | [Files with missing lines](https://app.codecov.io/gh/WeblateOrg/weblate/pull/11839?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=WeblateOrg) | Coverage Δ | | |---|---|---| | [weblate/api/serializers.py](https://app.codecov.io/gh/WeblateOrg/weblate/pull/11839?src=pr&el=tree&filepath=weblate%2Fapi%2Fserializers.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=WeblateOrg#diff-d2VibGF0ZS9hcGkvc2VyaWFsaXplcnMucHk=) | `92.57% <100.00%> (+0.10%)` | :arrow_up: | ... and [322 files with indirect coverage changes](https://app.codecov.io/gh/WeblateOrg/weblate/pull/11839/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=WeblateOrg)