graphics/proj: Update to 9.5.1

• Switch from PORTVERSION to DISTVERSION
• Use GitHub as primary site and osgeo.org as fallback
• Add devel/nlohmann-json to build dependencies
• Enable "make test"
• Minor changes to Makefile layout

Changelog: https://github.com/OSGeo/PROJ/releases/tag/9.5.1

PR: 283095
Reviewed by: lbartoletti (maintainer)