testLineSequence is flaky, at least on Linux

[jakepetroules]

testLineSequence occasionally fails on Linux. See attached test output which was from a run with nightly-main jammy on GitHub actions CI.

job-logs.txt

[jakepetroules]

Oddly I've never seen this fail on Darwin, but seems to happen quite often in Linux containers.

[jakepetroules]

One issue is that generateString shouldn't ever return an empty buffer, because a line ending with \r\n is indistinguishable from a line ending with \r followed by an empty line ending with \n. That's not the only problem though.

[jakepetroules]

Linux buffer size is 4096, macOS is 16384. I think on Linux we're getting unlucky that the middle of a newline sequence is right on the boundary of a multiple of a buffer size and thus we complete a line too early.