marsc 537 add cpu memory

[mcakircali]

Description

adds tests for logging statistics and unifies timeval conversions

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌦️ >> Documentation << 🌦️
https://sites.ecmwf.int/docs/dev-section/eckit/pull-requests/PR-291

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.44%. Comparing base (9daf037) to head (eb517bf).

Files with missing lines	Patch %	Lines
src/eckit/system/ResourceUsage.cc	0.00%	4 Missing ⚠️
src/eckit/log/ETA.cc	0.00%	1 Missing ⚠️
src/eckit/log/JSON.cc	0.00%	1 Missing ⚠️
src/eckit/log/Seconds.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #291      +/-   ##
===========================================
+ Coverage    66.42%   66.44%   +0.01%     
===========================================
  Files         1127     1128       +1     
  Lines        57992    57844     -148     
  Branches      4408     4408              
===========================================
- Hits         38522    38435      -87     
+ Misses       19470    19409      -61     

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