perf: further improve performance of ElementAwareArrayList

[triceo]

The goal here is to minimize the overhead of add/remove methods, as they showed up the highest in profiling in comparison to the original ElementAwareLinkedList.

[Copilot]

Pull request overview

This PR continues performance-focused work by optimizing ElementAwareArrayList internals (gap tracking/compaction and backing-array retention), refining tabu acceptor behavior (including deterministic fading-taboo decisions), and simplifying Bavet leaf indexing by removing the linked-list backend.

Changes:

• Reworked ElementAwareArrayList to avoid fail-fast iteration/modCount overhead, add compact() + firstGapPosition fast paths, and free large backing arrays when the list becomes empty.
• Updated tabu acceptors to use a new fading-taboo decision path with deterministic random consumption behavior; tightened configuration validation and tabu size constraints.
• Removed LinkedListLeafIndexer and switched indexer construction/tests to RandomAccessLeafIndexer.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
core/src/main/java/ai/timefold/solver/core/impl/util/ElementAwareArrayList.java	Optimizes gap handling/compaction, iterator behavior, and backing array retention/freeing.
core/src/test/java/ai/timefold/solver/core/impl/util/ElementAwareArrayListTest.java	Adds tests for compaction/first-gap behavior and backing-array free-path; adds randomized stress test.
core/src/main/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/AbstractTabuAcceptor.java	Refactors fading-taboo acceptance into a decision helper that can avoid consuming random in certain outcomes.
core/src/main/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/size/FixedTabuSizeStrategy.java	Enforces tabu size must be at least 1 and improves exception message.
core/src/test/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/size/FixedTabuSizeStrategyTest.java	Adds test coverage for invalid tabu sizes (0 and negative).
core/src/main/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/AcceptorFactory.java	Improves error messages, validates tabu acceptor configs, and removes duplicated configuration code.
core/src/test/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/AcceptorFactoryTest.java	Verifies factory rejects tabu acceptors without configured sizes.
core/src/test/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/ValueTabuAcceptorTest.java	Adds fading-taboo behavior test using deterministic TestRandom.
core/src/test/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/EntityTabuAcceptorTest.java	Adds fading-taboo behavior test using deterministic TestRandom.
core/src/test/java/ai/timefold/solver/core/impl/localsearch/decider/acceptor/tabu/MoveTabuAcceptorTest.java	Introduces move-taboo tests, including fading-taboo and aspiration scenarios.
core/src/main/java/ai/timefold/solver/core/impl/bavet/common/index/LinkedListLeafIndexer.java	Removed linked-list leaf backend implementation.
core/src/main/java/ai/timefold/solver/core/impl/bavet/common/index/LeafIndexer.java	Updates sealed permits to remove the deleted linked-list backend.
core/src/main/java/ai/timefold/solver/core/impl/bavet/common/index/IndexerFactory.java	Switches indexer backend creation to always use RandomAccessLeafIndexer.
core/src/test/java/ai/timefold/solver/core/impl/bavet/common/index/FusedEqualIndexTest.java	Updates fused equal index test to use RandomAccessLeafIndexer.

[zepfred]

Looks good to me. I have a few minor comments and some questions.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud