fix(bot): un-reacting from a poll never un-counted the vote

wyr/acronym/nhie/hottake tracked votes only on reaction-add, using
"add to bucket A, remove from bucket B" logic that self-corrects when
switching reactions but not when a reaction is simply removed — nio
never subscribed to RedactionEvent at all, so an un-react was
invisible to the bot. Fixes LotusGuild/matrix#6 (repro: react agree
and disagree, remove disagree, still counted as disagree).

Adds unrecord_* counterparts to each record_* vote function, a
reaction_id -> (poll_event_id, sender) index in Callbacks (only
populated for reactions on messages we're actually tracking, so it
stays bounded) so a later redaction can be traced back to what to
un-count, and wires up RedactionEvent -> callbacks.redaction in bot.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

matrixbot/bot.py

@@ -10,6 +10,7 @@ from nio import (
     InviteMemberEvent,
     LoginResponse,
     ReactionEvent,
+    RedactionEvent,
     RoomMemberEvent,
     RoomMessageText,
     UnknownEvent,
@@ -146,6 +147,7 @@ async def main():
     client.add_event_callback(callbacks.message, RoomMessageText)
     client.add_event_callback(callbacks.reaction, ReactionEvent)
     client.add_event_callback(callbacks.unknown_event, UnknownEvent)
+    client.add_event_callback(callbacks.redaction, RedactionEvent)
     client.add_event_callback(callbacks.member, RoomMemberEvent)
 
     # Accept invites only from trusted users, and decline the rest so they do