fix: consistent counts at proceedings and proceedings/attendees

[rjsparks]

This causes proceedings/attendees to show all attendees, not just those for whom the attendance is nomcom qualifying.

It refactors how attendance is calculated for proceedings, proceedings/attendees, and three_of_five_eligible9389

It fixes a bug (that had no consequence of previous nomcom choices) that counted hackathon only attendance towards nomcom eligibility.

I've independently checked that, except for the bug above which affected only two people, the results for three_of_five_eligible9389 remain unchanged for sets of 5 from [110...115] to [121...125].

Claude was used in creating this PR

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.52%. Comparing base (432aa3b) to head (e1a84da).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/meeting/models.py	88.88%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10935      +/-   ##
==========================================
+ Coverage   88.51%   88.52%   +0.01%     
==========================================
  Files         332      332              
  Lines       44970    44950      -20     
==========================================
- Hits        39805    39792      -13     
+ Misses       5165     5158       -7     

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[rpcross]

Possible proceedings/attendees/ view inconsistencies.

[rpcross]

Here registrations is being calculated separately and differently than stats so the totals may not match the table data. For example stats.onsite (from meeting.get_attendees().online) would include someone who registered onsite, did not checkin, and attended a session (Attended), whereas registrations would not.

[rjsparks]

Ok - the reconstruction of Registration objects here is overly complicated anyhow. e1a84da makes it wholly dependent on the people returned by get_attendees.