cl: Phase 6 packages — defpackage/in-package + pkg:sym — 518/518 tests

cl-packages dict, cl-current-package, cl-package-sep? strips pkg:
prefix from symbol/function lookups. defpackage/in-package/export/
use-package/import/find-package/package-name dispatch. Package-
qualified calls like (cl:car ...) and (cl:mapcar ...) work.
4 package tests added to stdlib.sx.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/common-lisp/tests/stdlib.sx

@@ -260,6 +260,24 @@
   (ev "(format nil \"(~{~A ~})\" (quote (1 2 3)))")
   "(1 2 3 )")
 
+;; ── packages ─────────────────────────────────────────────────────
+
+(check "defpackage returns name"
+  (ev "(defpackage :my-pkg (:use :cl))")
+  "MY-PKG")
+
+(check "in-package"
+  (ev "(progn (defpackage :test-pkg) (in-package :test-pkg) (package-name))")
+  "TEST-PKG")
+
+(check "package-qualified function"
+  (ev "(cl:car (quote (1 2 3)))")
+  1)
+
+(check "package-qualified function 2"
+  (ev "(cl:mapcar (function evenp) (quote (2 3 4)))")
+  (list true nil true))
+
 ;; ── summary ──────────────────────────────────────────────────────
 
 (define stdlib-passed passed)