Populate KeyValue Entry.created from message timestamp

[caspervonb]

KeyValue.get() hardcoded Entry.created to None, so callers had no creation time for a fetched key. Both the direct-get and API-get paths already carry the timestamp on RawStreamMsg.time; use it.

Fixes #398.

[synadia-claude-reviewer]

Claude finished @caspervonb's task in 1m 21s —— View job

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The fix is correct. _get() now passes msg.time (a datetime.datetime parsed from the server's ISO 8601 timestamp) into Entry.created for both the direct-get (direct=True) and API-get (direct=False) paths. This matches what the watcher path has always done (created=meta.timestamp in watch_updates).

One pre-existing issue worth fixing here: Entry.created is declared as Optional[int] at kv.py:95, but in practice it always holds a datetime.datetime (or None). Both the watcher path and this newly-fixed path store datetimes, and purge_deletes() already performs datetime arithmetic on it (entry.created subtracted from datetime.datetime.now(...)). The PR makes this mismatch more visible — worth correcting the annotation in the same change:

# kv.py line 95 — fix the annotation
created: Optional[datetime.datetime]

Test coverage is good: the new test exercises both direct=True and direct=False paths and asserts the type explicitly.