Keep single-line array bracket off a trailing comment line

[youdie006]

Summary

tomlkit.array().add_line("foo", comment="bar").as_string() produced [\n "foo", # bar] — the closing ] landed on the comment line, so the output failed to round-trip (tomlkit.loads(...) raised UnexpectedCharError). Fixes #580.

Array.as_string()'s single-line branch concatenated ] directly after the joined items. A trailing comment (from add_line(..., comment=...)) carries no newline, so the bracket was swallowed by the comment. This moves the bracket onto its own line when the last rendered element is a Comment; genuine single-line arrays ([1, 2, 3]) and multi-line arrays are byte-for-byte unchanged (the existing test_array_add_line assertion still passes).

Note: the issue suggested making add_line promote single-line arrays to multiline, but that reformats add_line(1, 2, 3) onto separate lines and breaks test_array_add_line, so the fix belongs in as_string, not add_line.

Added a regression test (test_array_add_line_single_line_comment_round_trips), verified red before the fix (UnexpectedCharError) and green after. pytest tests/test_items.py (87 passed) and ruff format --check pass locally.

Agent Drafting Metadata

• Agent: Claude Code
• Model: Claude (Opus)
• Notes: AI-assisted. The fix, the regression test, and this description were reviewed and verified locally by me (red-green cycle plus the full tests/test_items.py).