[client] Fix inverted awaitTermination condition in LookupClient#close

[XuQianJin-Stars]

The shutdown logic in LookupClient#close() had the awaitTermination condition inverted - it called shutdownNow() when the thread pool had already terminated gracefully, and did nothing when it timed out.

This is inconsistent with WriterClient#close() and all other shutdown patterns in the codebase which correctly negate awaitTermination() to trigger shutdownNow() on timeout.

The bug could cause the lookup sender thread pool to not be forcefully terminated when graceful shutdown times out, potentially leading to resource leaks.

Purpose

Fix a logic bug in LookupClient#close() where a missing ! operator caused inverted shutdown behavior for the lookup sender thread pool.

Brief change log

• Fixed the inverted awaitTermination() condition in LookupClient#close() by adding the missing ! negation operator, making it consistent with WriterClient#close() and the standard ExecutorService shutdown pattern documented in the Java SE docs.

Tests

• No new tests needed. This is a one-character fix (!) to an existing condition.
• The correct pattern is already validated by the existing shutdown behavior in WriterClient#close() and RemoteLogManager#shutdownAndAwaitTermination().

API and Format

• No API or format changes.

Documentation

• No documentation changes needed.