See https://github.com/Sija/raven.cr/issues/100 for the thing that triggered this
Caused by spotting this in the (shared on discord) logs of one of our users:
```
RuntimeWarning: DateTimeField Event.timestamp received a naive datetime (2025-10-26 16:01:08) while time zone support is active.
```
headers means: envelope headers and item headers.
Provides more robustness and a layer of defense-in-depth
Only those headers that we might rely on in a near future (event-based)
are included.
See #173
This is more canonical with stuff 'elsewhere on the internet'
we already did it behind-the-scenes for 'recommended gunicorn', so the
harmonization is in having the same default for the rest.
