fix(scheduler): apply a mid-replay CONFIG_PUSH to the sim limit plugin (bug-1964)

Cause: live applies every pushed config through sched_init_config(),
whose plugin_config_update() runs each plugin's config_hook (the limit
plugin builds its limits there). The simulator seeded the limit plugin
only at bootstrap (sim_bootstrap_limit_plugin()); the core's CONFIG_PUSH
event loaded groups, resources and queues but never told the plugins,
so a limit added during a replay never existed in sim.

Fix: one shared fan-out, plugin_config_update_core(core, config), which
live's plugin_config_update() now delegates to. The core's CONFIG_PUSH
calls a driver-registered xce_core_config_cb_t after loading groups (live
order), keeping the core free of plugin.c; the simulator registers the
fan-out in sim_bootstrap_limit_plugin(). limit_update_config() reads the
honestly-typed plugin->core instead of casting plugin->sched, so the hook
is safe on the sim core; the hand-built plugin fixtures in
test_limit_plugin.c/test_repl_limit_table.c now set plugin->core as
plugin_register() does. test_sim_limit_config_push_parity.c covers it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/scheduler/testsuite/test_limit_plugin.c

@@ -129,6 +129,9 @@ static void fixture_init(xce_scheduler_t* sched, xce_sched_plugin_t* plugin)
 
     memset(plugin, 0, sizeof(*plugin));
     plugin->sched = sched;
+    /* as plugin_register() sets it; limit_update_config() reads it
+     * (bug-1964) */
+    plugin->core = &(sched->core);
 
     rc = limit_init(plugin);
     TEST_ASSERT_EQUAL_INT(0, rc);