v3.2.1

• Introduces a shared internal BaseConverter and refactors Decimal/Hexadecimal/Base62 to use it.
• Renames/restructures PHPUnit tests and data providers for Base62 behaviors.
• Adds/updates repo hygiene and contributor/agent guidance files (.gitattributes, .editorconfig, .claude/*, Copilot instructions) and refreshes tooling configuration (composer.json, Makefile, phpstan).