Fixes newline

[pocopepe]

Closes #143

This fixes the p command so it matches GNU sed’s outputline() behavior.

write_chunk() now writes the line content without a trailing newline, and only appends \n if the original input line was newline-terminated (GNU’s chomped = true case). With this in place, the p command can simply call write_chunk() directly without any special handling.

To fully mirror GNU sed, this newline logic would ideally apply to all write_chunk() calls. However, doing so changes existing output behavior and breaks a large number of tests that currently depend on the old semantics. For now, this change is intentionally scoped to p to fix the reported issue without introducing broader regressions.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.26%. Comparing base (d57fca0) to head (d76dfd8).

Files with missing lines	Patch %	Lines
src/sed/processor.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
- Coverage   82.31%   82.26%   -0.05%     
==========================================
  Files          13       13              
  Lines        5371     5374       +3     
  Branches      293      294       +1     
==========================================
  Hits         4421     4421              
- Misses        948      951       +3     
  Partials        2        2              

Flag	Coverage Δ
macos_latest	82.70% <0.00%> (-0.05%)	⬇️
ubuntu_latest	82.81% <0.00%> (-0.05%)	⬇️
windows_latest	0.00% <0.00%> (ø)

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[sylvestre]

please add a test to make sure we don't regress in the future