sed: copy R text and e command output unchanged, as GNU sed does

[DePasqualeOrg]

Please ignore this PR until it is marked as ready for review

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GNU sed copies the line that R reads, and the output of the e command form, to the output exactly as they are. uutils sed treats them as lines and adds a newline when they lack one. With a file f that contains x and no newline, printf 'a\nb\n' | sed 'R f' prints x and b on separate lines, while GNU sed prints xb. Likewise, printf 'a\n' | sed '1e printf hi' prints hi on a line of its own, while GNU sed prints hia.

This PR adds OutputBuffer::write_raw, which writes a newline that the previous output line lacks and then the bytes unchanged, and uses it for appended text and e output. It also makes l print $ for an empty pattern space whose line lacked a newline, as GNU sed does.

codecov/patch fails only because CI does not count the coverage of tests that run the sed binary; it should pass after #591 is merged.

[codspeed]

Merging this PR will improve performance by 35.38%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 10 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	access_log_append	1.5 s	1.1 s	+35.38%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing DePasqualeOrg:fix-raw-r-and-e-output (35f178a) with main (1113479)}

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.91%. Comparing base (1113479) to head (35f178a).

Files with missing lines	Patch %	Lines
src/sed/processor.rs	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #590      +/-   ##
==========================================
+ Coverage   83.86%   83.91%   +0.04%     
==========================================
  Files          14       14              
  Lines        7203     7206       +3     
  Branches      424      423       -1     
==========================================
+ Hits         6041     6047       +6     
+ Misses       1157     1154       -3     
  Partials        5        5              

Flag	Coverage Δ
macos_latest	85.03% <75.00%> (+0.04%)	⬆️
ubuntu_latest	85.22% <75.00%> (+0.04%)	⬆️
windows_latest	0.00% <0.00%> (ø)

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[DePasqualeOrg]

Closing: this change is now part of #589, because each needed the other.