[Imkkey]

Fixes #148.

Replace the unguarded next() in restore_yaml_comments with a for/else loop that stops cleanly when a trailing comment block has no following key. Orphan trailing comments and blank lines are discarded. Column-zero comment detection remains unchanged so indented # lines inside literal or folded block scalars remain string data.

Add 18 cases covering trailing comments with and without final newlines, blank endings, comment-only/empty defaults, reordered keys, Configuration.dump() with overridden defaults, and literal/folded scalar round trips. Include an Unreleased changelog entry.

Related prior proposals: #61 by @hebote and #196 by @binggao1230, both closed without merging. This is a narrow iterator-exhaustion fix; it does not adopt broader indented-comment handling or change duplicate-key behavior.

Validation on Linux/Python 3.12.14, PyYAML 6.0.3:

• Before the fix, 12 added regression cases raise StopIteration; scalar-preservation controls pass.
• After: all 50 focused YAML/dump tests pass.
• Full suite after building docs: 318 passed, one pre-existing failure in test_bump_version_applies_sequential_changelog_updates. The same fixed-underline/current-date mismatch reproduces in a clean upstream worktree and is addressed separately in Make release changelog test independent of the date #211.
• Ruff lint/format, type checking for the package and changed test files, Sphinx HTML build with warnings as errors, documentation lint, changed-changelog formatting, and patch whitespace checks pass.
• Full-repository mypy on Python 3.12 still reports the baseline unused-ignore in test/test_valid.py:11; reproduced on unchanged upstream. Full-tree docstrfmt 2.0.1 now passes for all seven tracked RST files plus docs/conf.py, checked individually with --ignore-cache --pyproject-config pyproject.toml --check --no-format-python-code-blocks --preserve-adornments to avoid multiprocessing. The same checks pass on the clean upstream baseline.
• Independent differential check: outputs are unchanged for 23,405 previously successful generated inputs; 14,044 inputs previously raising StopIteration now return normally.

No Windows/other-Python run or remote CI pass is claimed. Prepared and checked with OpenAI Codex assistance; draft for maintainer review.