tar: restore SIGPIPE default so broken pipes exit 141 like GNU tar

[MsfPablo]

Fixes #263.

Problem

Rust's runtime ignores SIGPIPE by default, so when the reader of tar's stdout goes away (tar tf foo.tar | head -1), the resulting BrokenPipe error surfaced as a noisy TarError::Io on stderr with exit code 2. GNU tar dies silently via SIGPIPE with exit status 141.

Fix

Restore the default SIGPIPE disposition at startup (Unix only) so tar dies via SIGPIPE — exit status 141, no error output — matching GNU tar on all output paths (list, extract, create).

Testing

• cargo test: 62 passed (incl. new test_list_broken_pipe_exits_via_sigpipe, which lists an archive larger than a pipe through a closed reader and asserts death by SIGPIPE)
• Manual: tar -tf big.tar | head -1 now yields echo ${PIPESTATUS[0]} = 141 (was 2)

Assisted-by: Claude noreply@anthropic.com

[codspeed-hq]

Merging this PR will not alter performance

✅ 7 untouched benchmarks

---

_{Comparing MsfPablo:fix-brokenpipe-exit-code (f6fca2b) with main (d51f497)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.80%. Comparing base (791ae26) to head (f6fca2b).
⚠️ Report is 54 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #360      +/-   ##
==========================================
+ Coverage   96.84%   97.80%   +0.95%     
==========================================
  Files          11       15       +4     
  Lines        1492     1779     +287     
  Branches       29       34       +5     
==========================================
+ Hits         1445     1740     +295     
+ Misses         46       38       -8     
  Partials        1        1              

Flag	Coverage Δ
macos_latest	97.80% <100.00%> (+0.95%)	⬆️
ubuntu_latest	97.80% <100.00%> (+0.95%)	⬆️
windows_latest	0.00% <ø> (ø)

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