Fix linesLimited bypass when line completes in one chunk

[arimu1]

Summary

• text.linesLimited only checked stringBuilder.length after processing each chunk, so lines flushed into linesBuffer inside fillBuffers (when a line and its terminator arrive in the same chunk) bypassed the limit.
• Check completed lines in linesBuffer as well as the pending builder before emitting output.
• Add regression test covering single-chunk vs per-character chunking (repro from text.linesLimited lets through arbitrarily long lines when the line and its terminator land in the same chunk #3725).

Fixes #3725

Test plan

• sbt "coreJVM/testOnly fs2.TextSuite" — 92 tests passed (JDK 17)
• New test: linesLimited rejects long lines completed in a single chunk

Made with Cursor

[arimu1]

Note for maintainers/CI watchers: the red root* / Native jobs on the opening push look like GitHub Actions infra (Homebrew unknown install step: run / bootstrap), not product assertions from this change. Local TextSuite was green when opened. Happy to re-run when the matrix is healthy.