Preserve end-of-line comment whitespace when editing `pyproject.toml` (#16734)
Resolves https://github.com/astral-sh/uv/issues/16719
`uv add` collapses multiple spaces before inline comments in
`[project.dependencies]`, causing unrelated diffs and moving comments
onto the wrong columns. This diff captures the exact whitespace padding
that preceded each end-of-line comment when parsing the array and reuses
it when formatting.
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Co-authored-by: konstin <konstin@mailbox.org>