Description

Fix body_length_limit so it preserves intentional blank lines in commit bodies while still wrapping non-empty lines to the configured width.

Checklist

• I have read the contributing guidelines

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: GitHub Copilot CLI following the guidelines

Code Changes

• Add test cases to all the changes you introduce
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes — not required, just a fix

Documentation Changes

• Run uv run poe doc locally to ensure the documentation pages renders correctly — no documentation changes
• Check and fix any broken links (internal or external) — no documentation changes

Expected Behavior

With body_length_limit enabled, Commitizen should preserve blank lines in the commit body and only wrap long non-empty lines.

Steps to Test This Pull Request

1. Configure body_length_limit = 80 or run cz commit --body-length-limit 80.

2. Create a commit message body with a paragraph break, for example:

   First paragraph line
   
   Second paragraph line
   

3. Confirm the generated commit message still contains the blank separator line.

4. Run uv run pytest tests/commands/test_commit_command.py -k body_length_limit.

5. Run uv run ruff check commitizen/commands/commit.py tests/commands/test_commit_command.py.

6. Run uv run ruff format --check commitizen/commands/commit.py tests/commands/test_commit_command.py.

Additional Context

This fixes a regression where textwrap.wrap("") caused empty body lines to be dropped when body_length_limit was enabled (#2079).