refactor: Use tox memory in group chats allocations.

[iphydf]

This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 73.01587% with 34 lines in your changes missing coverage. Please review.

Project coverage is 72.90%. Comparing base (a749ee7) to head (52a2c1a).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
toxcore/group_chats.c	73.01%	34 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2818      +/-   ##
==========================================
- Coverage   73.13%   72.90%   -0.24%     
==========================================
  Files         150      150              
  Lines       30702    30706       +4     
==========================================
- Hits        22454    22385      -69     
- Misses       8248     8321      +73     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.