fix: has_events_marked to check actual bits, not just key existence

[chiara-doist]

Description

My understanding of the problem:

• has_events_marked was checking for key existence only (I've changed to actually check the values within).
• This is because select2 is using a BitOp (ref ⬇️), and these operations create keys even when no bits are set.

bitmapist/bitmapist/cohort/__init__.py

Lines 301 to 309 in 33aeeb1

	# events for select2 (+select2b)
	select2_events = fn_get_events(select2, delta_now, system)
	if select2b:
	select2b_events = fn_get_events(select2b, delta_now, system)
	select2_events = BitOpAnd(system, select2_events, select2b_events)
	if not select2_events.has_events_marked():
	result.append("")
	continue

Reference

• https://github.com/Doist/Issues/issues/18423

[lefcha]

Looks good to me!

[jacobo-doist]

Whoa, brilliant, I threw Claude at this aggressively and ended up getting misdirected every time. Great find!

[amix]

Neat fix 👌 I also love that you added test cases