Set up COPR repository for testing builds

[miabbott]

Create a COPR repository to build and test the RPM package before submitting to Fedora.

Tasks

• Create COPR project for tar-diff
• Configure automated builds from GitHub releases or tags
• Test installation on Fedora 42, 43, Rawhide

Acceptance Criteria

• COPR builds succeed
• Package installable via dnf copr enable <repo> && dnf install tar-diff

Dependencies

• Depends on Create RPM spec file for Fedora packaging #39 (RPM spec file)