_send_reaction now returns Optional[str] (event_id) instead of bool.
Tests updated:
- test_send_reaction: assert result == event_id string
- test_send_reaction_no_client: assert result is None
- test_on_processing_start_sends_eyes: _send_reaction returns event_id,
now also asserts _pending_reactions is populated
- test_on_processing_complete_sends_check: set up _pending_reactions and
mock _redact_reaction, assert eyes reaction is redacted before sending check
58413c411f