fix: Consult cgroups to determine free memory

[gasmith]

Fixes #15797

[codspeed-hq]

CodSpeed Performance Report

Merging #15798 will not alter performance

_{Comparing gasmith:sysinfo-cgroups (62f5dec) with main (d11da5e)}

Summary

✅ 22 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.39%. Comparing base (4a870cc) to head (62f5dec).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15798      +/-   ##
==========================================
- Coverage   81.36%   80.39%   -0.97%     
==========================================
  Files        1379     1264     -115     
  Lines      176828   165423   -11405     
  Branches     2543        0    -2543     
==========================================
- Hits       143875   132998   -10877     
+ Misses      32471    32425      -46     
+ Partials      482        0     -482     

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[ritchie46]

Yeap, seems fine. Thanks