Poll when the stream signals a session boundary

[rhammen]

ChargerCurrentUserUuid (722) and CompletedSession (723) are never pushed
over the live stream, so they only change on a poll — 10 minutes apart while
the charger is idle. A short authorized session can fall between two polls and
never show up at all. The sensors from #431 read 722 directly.

ChargerOperationMode (710) and SessionIdentifier (721) do stream, and
change on the same session boundaries. stream_callback now runs the existing
coordinator poll sequence ([2, 7, 15] s) when either arrives. trigger_poll
cancels an in-flight sequence, so a burst of frames collapses into one.

Any 710 value triggers, not only Disconnected: a plug-in is where authorization
becomes relevant, and the extra polls on charging transitions are a handful per
session against the 60 s charging interval.

Verified on a Go 2 (fw 3.3.0.0), unplug then plug back in:

+0.0 s   710 → Disconnected          streamed
+2.1 s   722 cleared                 poll 1
+7.1 s   CompletedSession updated    poll 2  (not yet available at +2 s)

An app authorization later in the same session was visible on 722 about 2 s
after its 721 frame. Without this, both wait for the next 10-minute poll; a 25 s
session on 2026-09-09 was missed entirely.

Clearing 722 at session end still relies on #425 — this only makes it appear
sooner.

#418 also adds tests/test_manager.py; the two files are disjoint, whoever
merges second concatenates.

Fixes #432

🤖 Generated with Claude Code

[sveinse]

Please resolve the conflicts in this PR. Thanks.