[lake/iceberg] Fix listener leak in IcebergLakeCommitter

[Guosmilesmile]

Purpose

Because Iceberg's Listeners registry is:

• JVM-global (a static Map<Class, Queue<Listener>>),
• append-only (no deregister / unregister API),

every newly created IcebergLakeCommitter permanently appended one more
listener to the global queue. In a long-running tiering job, the queue keeps
growing and every CreateSnapshotEvent is dispatched to all of them,
causing:

1. Memory leak – listener instances are never garbage-collected as long
   as the Listeners class is loaded.
2. CPU overhead – each Iceberg commit triggers N listener notifications,
   where N grows over time.
3. Correctness risk for shared catalogs – when multiple IcebergLakeCommitter instances live in the same JVM (e.g. multiple tiering tasks), all of their listeners write to the same ThreadLocal<Long> currentCommitSnapshotId. The last writer wins, but the duplicated work is still wasted.

Brief change log

• Move listener registration from the constructor to a static {} block in
  IcebergLakeCommitter, so the listener is registered exactly once per
  ClassLoader (effectively once per JVM).
• Keep the ThreadLocal#remove() call after each commit so no thread-local
  entry is leaked across commits.
• Add IcebergLakeCommitterListenerLeakTest which:
  • Reflectively reads the private Listeners.LISTENERS registry.
  • Creates multiple IcebergLakeCommitter instances.
  • Asserts that the number of IcebergSnapshotCreateListener instances in the registry stays at exactly 1, regardless of how many committers are constructed.

Tests

The behavior is already coverd by existing test.

API and Format

No public API or storage format change.

Documentation

No documentation change; behavior-only fix.

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[luoyuxia]

@Guosmilesmile Thanks for the pr. lgtm overall. I only left one comment

[luoyuxia]

Can we just remove this test since it's a trival change and the behavior is already coverd by existing test

[Guosmilesmile]

Sure, remove IcebergLakeCommitterListenerLeakTest.

[luoyuxia]

Thanks. LGTM

[Guosmilesmile]

Thanks @luoyuxia for reviewing !