seen: modify/fix stored value & delta calculation for Aware trigger.time

[dgw]

Description

Fixes a bug on master reported on IRC by monaco (@hedho), related to trigger.time changes from #2099.

I chose to eliminate the bug by using Unix timestamps instead of datetime objects. <datetime_obj>.timestamp() has been around since Python 3.3, so we're safe to use it with 8.x's minimum requirement of Python 3.7.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches

[Exirel]

I think it would be best to add this change (line 68):

- bot.db.set_nick_value(nick, 'seen_timestamp', time.time())
+ bot.db.set_nick_value(nick, 'seen_timestamp', trigger.time.timestamp())

[dgw]

@Exirel That's not related to fixing the bug, though.

Docs for the datetime.timestamp() method specifically say it returns a value "similar to that returned by time.time()". Is there a practical reason for this change other than storing when the line was sent (or received, on nets without server-time) instead of when the seen plugin processes it? The small difference in precision when reporting the time delta later is meaningless at the scale of this plugin's normal use (days or weeks later).

[Exirel]

Yeah, but it's a good opportunity to be more coherent with the feature. trigger.time is timezone sensitive, and I feel like it makes more sense to use it here as well. Beside, if the event comes from the IRC history (if that ever get implemented), we won't have to update the seen plugin (at least, not that part).

[dgw]

trigger.time is timezone sensitive

Well, this is annoying, but not because of what you said. It's annoying that time.time() isn't always in UTC. Interactive Python session below, which made me quite irritated for a few minutes. 😅

Give me a moment to update the patch.

>>> import time
>>> from datetime import datetime
>>> t = time.time(); dt = datetime.now()
>>> t
1646690791.7546873
>>> dt.timestamp()
1646690791.754754
>>> import pytz
>>> dt.replace(tzinfo=pytz.utc).timestamp()
1646669191.754754