fix: use config snapshot in NacosConfigDataLoader to fix stale config in cluster mode

Fixes #4296. The config snapshot mechanism from PR #3644 was not applied to the
Spring Boot 3.x ConfigData API path (NacosConfigDataLoader). In Nacos cluster mode,
when a config change notification arrives from one node but the fetch goes to another
node that hasn't synced yet, the client gets stale config.

Assisted-by: Hermes Agent

Author: EvanYao826

spring-cloud-alibaba-starters/spring-alibaba-nacos-config/src/main/java/com/alibaba/cloud/nacos/configdata/NacosConfigDataLoader.java

@@ -154,9 +154,14 @@ private List<PropertySource<?>> pullConfig(ConfigService configService, String g
 			throws NacosException, IOException {
 		String config = NacosSnapshotConfigManager.getAndRemoveConfigSnapshot(namespace,
 				dataId, group);
-		if (config == null) {
+		if (config == null || config.isEmpty()) {
 			config = configService.getConfig(dataId, group, timeout);
 		}
+		else {
+			log.debug(String.format(
+					"[Nacos Config] Load config from snapshot[dataId=%s, group=%s]",
+					dataId, group));
+		}
 		logLoadInfo(group, dataId, config);
 		// fixed issue: https://github.com/alibaba/spring-cloud-alibaba/issues/2906 .
 		String configName = group + "@" + dataId;