Add validation for --line-ranges values

[avasis-ai]

Summary

The parse_line_ranges function previously accepted invalid ranges without raising errors:

• "5-3" where START > END
• "0-5" or "-1-5" with non-positive line numbers

This adds validation to raise a clear ValueError with a descriptive message when invalid ranges are provided, instead of silently accepting them and producing unexpected formatting behavior.

Test Plan

Added test_parse_line_ranges_valid and test_parse_line_ranges_invalid parametrized tests in tests/test_ranges.py covering:

• Valid ranges: single, same start/end, multiple ranges
• Invalid ranges: reversed (start > end), zero, negative

[cobaltt7]

Thanks @avasis-ai! Please add a changelog entry and add types to the tests.

[github-actions]

diff-shades results comparing this PR (4adf522) to main (35921ac):

--preview style: no changes

--stable style: no changes

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