use std::error_code instead of system::error_code

[ashtum]

Closes #162

[cppalliance-bot]

An automated preview of the documentation is available at https://163.beast2.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-08-26 19:11:17 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.10%. Comparing base (6d83768) to head (49f8d8f).
⚠️ Report is 58 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #163       +/-   ##
============================================
+ Coverage    51.11%   93.10%   +41.99%     
============================================
  Files           37        3       -34     
  Lines         1528       87     -1441     
============================================
- Hits           781       81      -700     
+ Misses         747        6      -741     

Flag	Coverage Δ
linux	93.10% <ø> (?)

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see 13 files with indirect coverage changes

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