find: skip broken pipe errors in wasm executions

[aki-kong]

Fixes #801.

out.flush().unwrap() in Printer::print panics when stdout is a
closed pipe (e.g. find . | head -5), since the flush fails with
EPIPE. Only visible on wasm32-wasip1: there's no SIGPIPE there, so
the write error reaches this unwrap() and panics. On native Linux
the same unguarded unwrap() exists, but SIGPIPE usually kills the
process before this code runs, so the bug goes unnoticed.

Treat io::ErrorKind::BrokenPipe on write!/flush() as expected
and exit 0, instead of panicking.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.93%. Comparing base (6ef1fd6) to head (965d734).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #802      +/-   ##
==========================================
+ Coverage   91.90%   91.93%   +0.03%     
==========================================
  Files          35       35              
  Lines        7248     7251       +3     
  Branches      376      378       +2     
==========================================
+ Hits         6661     6666       +5     
+ Misses        444      443       -1     
+ Partials      143      142       -1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[codspeed-hq]

Merging this PR will not alter performance

✅ 20 untouched benchmarks

---

_{Comparing aki-kong:fix/find-wasm-pipe-break (965d734) with main (6ef1fd6)}

[github-actions]

Commit 18052b1 has test result changes:

bfs testsuite:

Test results comparison:
  Current:   TOTAL: 314 / PASSED: 265 / FAILED: 43 / SKIPPED: 6
  Reference: TOTAL: 315 / PASSED: 267 / FAILED: 42 / SKIPPED: 6

Changes from main branch:
  TOTAL: -1
  PASSED: -2
  FAILED: +1

New test failures (2):
  - gnu/exec_flush_fail
  - gnu/print_error

Test improvements (1):
  + gnu/files0_from_ok

[sylvestre]

could you please add a test to make sure it doesn't regress ?

[aki-kong]

could you please add a test to make sure it doesn't regress ?

I've tried fixing the new test failures from the bfs test suite. Also added the regression tests. Let me know if it is good to go.

[github-actions]

Commit 965d734 has test result changes:

bfs testsuite:

Test results comparison:
  Current:   TOTAL: 313 / PASSED: 267 / FAILED: 40 / SKIPPED: 6
  Reference: TOTAL: 315 / PASSED: 267 / FAILED: 42 / SKIPPED: 6

Changes from main branch:
  TOTAL: -2
  PASSED: +0
  FAILED: -2

Test improvements (2):
  + gnu/files0_from_ok
  + gnu/okdir_path_empty