v1.6.0

CssXPath now supports GT\CssXPath, with the existing Gt\CssXPath namespace kept for compatibility. The release also tidies up the development tools and coverage reporting.

• 1c26b974 Codecov v6.
• b1992d23 Update Composer configuration.
• a8682004 Support GT\CssXPath alongside the legacy namespace.
• bc6a61af Fix code coverage.