test(anvil): trace PR 760 mutation memory

[martin-kolinek]

Purpose

Diagnose the Linux mutation-runner shutdown on #760.

The original run selected 4,990 mutants, passed its baseline, then the Linux runner received SIGTERM/exit 143 without a cargo-mutants result.

Diagnostic changes

• diff mutation testing against feat(http_headers): add typed HTTP header parsing #760's original base (ec1f6bc2)
• run mutations sequentially with --jobs 1
• stream Linux system memory and largest process RSS values every two seconds

This intentionally changes generated Anvil files only for diagnosis and is not intended as the permanent fix.

Evidence

Original cancelled Linux job: https://github.com/microsoft/oxidizer/actions/runs/35132948246/job/105098807908

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.9%. Comparing base (74f116f) to head (77a855c).

Additional details and impacted files

@@             Coverage Diff              @@
##           http_headers    #766   +/-   ##
============================================
  Coverage          99.9%   99.9%           
============================================
  Files               710     710           
  Lines             96880   96880           
============================================
  Hits              96876   96876           
  Misses                4       4           

Flag	Coverage Δ
linux	99.9% <ø> (ø)
linux-arm	99.9% <ø> (ø)
windows	99.9% <ø> (ø)

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