Functions to truncate time types

During tests I insert an entity in PostgreSQL (which has microsecond resolution) with a timestamp created with `time` (which has picosecond resolution). When I fetch the entity from the database, the timestamps obviously differ, because PostgreSQL has lower precision:

```diff
- expiration = Just 2025-08-22 11:59:23.370617513 UTC}]
+ expiration = Just 2025-08-22 11:59:23.370617 UTC}]
```

I have the option to tweak the record before handing it to the `assertEqual` funtion in my test suite. I was wondering if I could remove some precision from `UTCTime` in a principled way. Is that advised?

(btw, thank you @AshleyYakeley for your work on this library!)