pr: stream simple layouts for non-file inputs

[mattsu2020]

Summary

This PR adds a streaming path for simple pr layouts when reading from non-file inputs such as FIFOs and character devices.

The main goal is to avoid buffering the entire input in memory for cases where pr can process the input line by line. This also makes inputs like /dev/zero start producing output immediately instead of waiting for a full read.

What changed

• add a streaming implementation for simple pr layouts

• use the streaming path for supported non-file inputs

• align streaming output with the existing buffered behavior, including page trailer formatting

• validate UTF-8 incrementally while streaming and report invalid input cleanly

• fall back to the buffered path when the selected page layout leaves no printable content lines

• add regression tests for:

  • character-device input
  • invalid UTF-8 from a FIFO
  • FIFO/file parity in zero-content-line edge cases

  related

  pr /dev/zero [SIGPIPE|SIGKILL] #11139

[sylvestre]

the list of commits isn't ideal, could you please improve it? thanks

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!
Congrats! The gnu test tests/tail/pipe-f is now passing!

[codspeed-hq]

Merging this PR will improve performance by 3.64%

⚡ 1 improved benchmark
✅ 297 untouched benchmarks
⏩ 48 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	du_summarize_balanced_tree[(5, 4, 10)]	6.7 ms	6.5 ms	+3.64%

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_{Comparing mattsu2020:pr_zero (8a28cc6) with main (995c9e0)}

Footnotes

1. 48 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩