Add collation_key_buffer (arena) and collation_key_ends (offsets) to
LineData and RecycledChunk, with a collation_key() accessor. All sort
keys for a chunk are stored in a single Vec<u8> to avoid millions of
small heap allocations.
The `+1` accounting for the ACL/context indicator was applied once per
item inside the padding loop, so N files with ACLs inflated the
link-count column width by N. Apply it a single time after the loop.
Fixes#10980
test_single_quote_pair_as_delimiter_is_invalid is intermittent on
i686: the parent writes "a''b\n" to cut's stdin while cut validates
args and exits immediately with "delimiter must be a single
character". On a fast child exit, the kernel closes the pipe
read-end before the parent's write() runs, so write() returns
EPIPE and the pipe_in thread panics.
The race is inherent: draining stdin in cut before exiting on an
arg error would hang on terminals and read unbounded data from
long pipes, contradicting GNU behavior. Use the test framework's
ignore_stdin_write_error() flag, which exists for exactly this
"parent writes to child that exits fast" pattern.
Upstream commit 9f50c8b42 ("tee: fix input with sleep") already
contains the functional fix for short reads from a paused writer.
Keep the regression coverage so we do not reintroduce the bug.
The test writes one small chunk, waits long enough for a buggy tee to
exit, then writes a second chunk and asserts both stdout and the output
file receive both writes.
