test: csf.pl testability suite

[zeroth-blip]

Summary

• port cpanel/cpanel-csf commit 1c80b71 into the zeroth fork's current layout
• make csf.pl loadable as a module for tests while keeping normal CLI execution via run() unless caller()
• add csf.pl coverage under .github/tests/unit/ plus the uninitialized-warning regression test
• add a dedicated MockConfig test helper and limit extra CI Perl deps to only the new csf-related tests

Notes

• this is adapted to the current BlackHOST/zeroth test layout, not a literal path-for-path cherry-pick from cPanel
• Claude review feedback was applied before commit, including the modulino guard, lighter open3 wrapper, repo test helper usage, and narrower CI dependency installation

[zeroth-blip]

Closing this and reworking it from scratch to avoid licensing issues.