lisp: split off lisp_free as it's own function

lisp_free will do a shallow clean of any object, freeing its
associated memory.  It won't recur through any containers, nor will it
freakout if you give it something that is constant (symbols, small
integers, NIL, etc).

src/lisp.c

@@ -34,26 +34,7 @@ void sys_free(sys_t *sys)
   for (size_t i = 0; i < VEC_SIZE(&sys->memory, lisp_t **); ++i)
   {
     lisp_t *allocated = VEC_GET(&sys->memory, i, lisp_t *);
-    switch (get_tag(allocated))
-    {
-    case TAG_CONS:
-      // Delete the cons
-      free(as_cons(allocated));
-      break;
-    case TAG_VEC:
-    {
-      vec_t *vec = as_vec(allocated);
-      vec_free(vec);
-      free(vec);
-      break;
-    }
-    case TAG_NIL:
-    case TAG_INT:
-    case TAG_SYM:
-    case NUM_TAGS:
-      // shouldn't be dealt with (either constant or dealt with elsewhere)
-      break;
-    }
+    lisp_free(allocated);
   }
 
   // Free the container
@@ -110,6 +91,30 @@ lisp_t *cdr(lisp_t *lsp)
     return CDR(lsp);
 }
 
+void lisp_free(lisp_t *item)
+{
+  switch (get_tag(item))
+  {
+  case TAG_CONS:
+    // Delete the cons
+    free(as_cons(item));
+    break;
+  case TAG_VEC:
+  {
+    vec_t *vec = as_vec(item);
+    vec_free(vec);
+    free(vec);
+    break;
+  }
+  case TAG_NIL:
+  case TAG_INT:
+  case TAG_SYM:
+  case NUM_TAGS:
+    // shouldn't be dealt with (either constant or dealt with elsewhere)
+    break;
+  }
+}
+
 /* Copyright (C) 2025, 2026 Aryadev Chavali
 
  * This program is distributed in the hope that it will be useful, but WITHOUT