AHaldner/mailcheck: v1.3.0

Features

• improve DKIM selector handling and reporting
• add —no-cache flag to disable DNS lookup caching

Fixes

• update DMARC and DKIM test expectations and logic

Refactors

• rework help formatting to use flag metadata structs

Docs

• document —no-cache flag and update usage examples
• update changelog for v1.2.0

Other

• Merge pull request #2 from AHaldner/fixes