pr: stream -o/--indent offset to avoid abort on large values

[TheAdamWarlock]

Fixes #12978.

pr -o N (--indent) aborted on large offsets that fit in i32 (e.g. -o 999999999) because the indent was built as " ".repeat(n), allocating an N-byte string up front that fails under limited memory. The change stores the offset as a count and streams the spaces in 256-byte chunks at print time, so peak memory is constant and output is unchanged. Adds a regression test that runs pr with a large offset under a small memory cap and checks it exits cleanly.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/retry (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!