Fix DeprecationWarning in timeutils.py and archive.py

```
commoncode/timeutils.py:61: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
datim = dt or datetime.utcnow()
```
```
commoncode/archive.py:61: DeprecationWarning: Python 3.14 will, by default, filter extracted tar archives and reject files or modify their metadata. Use the filter argument to control this behavior.
tar.extractall(target_dir, members=to_extract)
```