refactor: free more reachable memory with EXITFREE (#26349)

Discovered using __sanitizer_print_memory_profile().

src/nvim/eval.c

@@ -500,6 +500,10 @@ static void evalvars_clear(void)
       p->vv_list = NULL;
     }
   }
+
+  partial_unref(vvlua_partial);
+  vimvars[VV_LUA].vv_partial = vvlua_partial = NULL;
+
   hash_clear(&vimvarht);
   hash_init(&vimvarht);    // garbage_collect() will access it
   hash_clear(&compat_hashtab);