leaf-handler-vc: Add package to package-selected-packages

[uwabami]

Description

The :vc handler (leaf-handler-vc) previously only called package-vc-install but did not update package-selected-packages. This caused packages installed via :vc to be flagged as orphaned by package-autoremove.

This commit adds a leaf-safe-push call to leaf-handler-vc, aligning its behavior with leaf-handler-package. This ensures that VC-installed packages are correctly registered in the in-memory session, preventing them from being unexpectedly removed during package cleanup.

;; Before
(leaf-handler-vc bbdb (bbdb (:url "..." :lisp-dir "...")))
;; => (unless (package-installed-p 'bbdb) (package-vc-install '(bbdb ...) nil))

;; After
(leaf-handler-vc bbdb (bbdb (:url "..." :lisp-dir "...")))
;; => (progn
;;      (leaf-safe-push 'bbdb package-selected-packages 'no-dup)
;;      (unless (package-installed-p 'bbdb) (package-vc-install '(bbdb ...) nil)))

Checklist

• I've read CONTRIBUTING.org.
  • I've assign FSF. -> I alerady send e-mail, wating response.
  • The leaf.el after my changed pass all testcases by make test.
  • My changed elisp code byte-compiled cleanly.
  • I've added testcases related to my PR.
    • No. Because current test suites do not check for leaf handler-* macro expansion.
  • I've fixed README related the my added testcases.
    • No. Because I didn't add any test casees.

[uwabami]

Checklist

• I've read CONTRIBUTING.org.
  • I've assign FSF. -> I alerady send e-mail, wating response. done!
  • The leaf.el after my changed pass all testcases by make test.
  • My changed elisp code byte-compiled cleanly.
  • I've added testcases related to my PR.
    • No. Because current test suites do not check for leaf handler-* macro expansion.
  • I've fixed README related the my added testcases.
    • No. Because I didn't add any test casees.

[conao3]

@uwabami Thanks!