Fix infinite loop in Parser.with_names and improve "source" column handling in Parser.columns

What's Changed

• Bump actions/cache from 4 to 5 by @dependabot[bot] in #600
• Bump sqlparse from 0.5.4 to 0.5.5 by @dependabot[bot] in #601
• Bump dependabot/fetch-metadata from 2.4.0 to 2.5.0 by @dependabot[bot] in #602
• Parser.columns drops column named source when it is the last column in a SELECT statement by @macbre in #603
• Drop Python 3.9 support by @macbre in #604
• Fix infinite loop in Parser.with_names for malformed WITH statements by @macbre in #605
• Add AGENTS.md documentation for developers and AI agents by @macbre in #606

Full Changelog: v2.19.0...v2.20.0