fix: more accurate group areas (red API)

[jennifer-richards]

In the red / errata API, only show area for IETF stream docs whose group parent has type_id="area". Only include area ADs if the area is currently active.

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.35%. Comparing base (8005a8b) to head (a948030).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/doc/serializers.py	27.27%	8 Missing ⚠️
ietf/group/serializers.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10462      +/-   ##
==========================================
- Coverage   88.36%   88.35%   -0.02%     
==========================================
  Files         325      325              
  Lines       43653    43719      +66     
==========================================
+ Hits        38576    38627      +51     
- Misses       5077     5092      +15     

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