Include cluster name in WAGED async rebalance thread names

[LZD-PratyushBhatt]

The async baseline and best-possible calculation tasks run on single-thread executors with default JVM thread names (pool-N-thread-1), so WAGED rebalance failure logs lose cluster context when a single controller JVM hosts multiple WAGED-managed clusters. This makes correlating errors across clusters in shared log stores difficult.

Rename the executor thread to WagedGlobalRebalance- / WagedPartialRebalance- for the duration of each task and restore the original name in a finally block (the executor's single thread is reused across submissions, so restoration prevents stale names from leaking into the next task). Also include the cluster name explicitly in the LOG.error messages for easier grep.

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