[BUG] ThreadPoolExecutor never shut down in close0 for Huawei, Tencent, and Aliyun SLS clients

- severity: High
- files: `shenyu-plugin/shenyu-plugin-logging/shenyu-plugin-logging-huawei-lts/src/main/java/org/apache/shenyu/plugin/huawei/lts/client/HuaweiLtsLogCollectClient.java:103,117-126`; `.../shenyu-plugin-logging-tencent-cls/.../TencentClsLogCollectClient.java:93,112-121`; `.../shenyu-plugin-logging-aliyun-sls/.../AliyunSlsLogCollectClient.java:96,114-120`
- description: Each client creates a `ThreadPoolExecutor` (`threadExecutor`) in `initClient0()` for `Futures.addCallback(...)`. `close0()` only shuts down the producer/client and never calls `threadExecutor.shutdown()`. `AbstractLogConsumeClient.initClient()` calls `close()` before re-init, so every config refresh leaks the old thread pool's threads.
- impact: Thread leak on every config refresh or plugin re-init; eventually `RejectedExecutionException` and no log delivery.
- suggested_fix: Add `threadExecutor.shutdown()` to each `close0()`.
- confidence: High
- related_existing: none

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_Identified during the 2026-08-02 deep re-scan; full list in [`docs/scan2-2026-08-02/00-consolidated-critical-high.md`](docs/scan2-2026-08-02/00-consolidated-critical-high.md)._

Start with initClient0() and close0() in HuaweiLtsLogCollectClient.java, TencentClsLogCollectClient.java, and AliyunSlsLogCollectClient.java at the referenced lines, then read AbstractLogConsumeClient.initClient() to understand the re-initialization path. Ensure each close0() shuts down its threadExecutor, and verify that configuration refreshes no longer retain the old executor threads.

Written by the indexing model from the issue text.