Fix delayed operator memory release after fragment termination

[Caideyipi]

Description

Problem

Fragment-instance state listeners run on a shared bounded notification executor. The operator-memory estimate reserved by LocalExecutionPlanner was returned from one of those asynchronous listeners.

A fragment can report a fast execution failure, such as a SELECT INTO type mismatch, while notification threads are still closing drivers for earlier fragments. Consecutive failures can therefore accumulate completed fragments' admission reservations and eventually fail with a false memory-insufficient error.

Design

• Add FragmentInstanceStateMachine.addFinalStateChangeListener for short, non-blocking bookkeeping that must finish in the thread performing the terminal transition. It invokes each pre-registered listener exactly once and invokes late registrations immediately.
• Return the operator-memory estimate through this synchronous final-state listener.
• Move the existing lightweight fragment statistics and DataNodeQueryContext cleanup to the same path.
• Keep driver closing, file-handle release, exchange-pool deregistration, and other potentially blocking cleanup on the existing asynchronous listener.

This fixes all fast fragment termination paths (finished, failed, canceled, and aborted), rather than special-casing SELECT INTO or increasing test memory.

Tests

• mvn spotless:check -pl iotdb-core/datanode
• FragmentInstanceStateMachineTest
• FragmentInstanceContextTest
• LocalExecutionPlannerOperatorsMemoryTest

The three unit-test classes pass 20 tests. The new regression test deliberately uses a notification executor that never runs and verifies that terminal bookkeeping and operator-memory release still complete synchronously.

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This PR has:

• been self-reviewed.
  • concurrent read and write
• added Javadocs for the new non-trivial method.
• added comments explaining why synchronous bookkeeping is required.
• added unit tests covering the new code paths.

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Key changed/added classes

• FragmentInstanceStateMachine
• FragmentInstanceContext
• LocalExecutionPlanner