refactor: don't use filesystem for group aliases

[jennifer-richards]

This one is performant enough I don't think caching is needed.

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.93%. Comparing base (187c2c5) to head (70aa17c).
Report is 246 commits behind head on main.

❗ Current head 70aa17c differs from pull request most recent head 068cf1a

Please upload reports for the commit 068cf1a to get more accurate results.

Files	Patch %	Lines
ietf/group/utils.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7556      +/-   ##
==========================================
- Coverage   88.98%   88.93%   -0.06%     
==========================================
  Files         291      295       +4     
  Lines       40717    41231     +514     
==========================================
+ Hits        36233    36668     +435     
- Misses       4484     4563      +79     

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