fix: remove stray newlines from inheritance printer

[timeless-hayoka]

Fixes the inheritance printer linebreak regression reported in #1835.

What changed:

• removed the misplaced newline concatenation in the inheritance printer
• kept the existing structured output fields intact
• added a regression assertion that the printer description does not contain carriage returns

Verification:

• uv run pytest tests/e2e/printers/test_printers.py -k inheritance

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Gemini seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}