chore: remove support for the identity map from the value range cache

[zepfred]

No description provided.

[Copilot]

Pull request overview

This PR removes identity-based caching/indexing behavior in value range infrastructure, standardizing lookups and deduplication on equals/hashCode semantics across value range caches and related indexing.

Changes:

• Simplified ValueRangeCache by removing the builder/trusted-vs-user modes and introducing of(...) factory methods backed by standard hash-based collections.
• Removed isValueImmutable plumbing from collection/composite value ranges and stopped using immutability to decide identity vs equals-based maps in ValueRangeState.
• Updated/extended unit tests to assert contains() works for different instances that are equal by planning ID/code.

Reviewed changes

Copilot reviewed 10 out of 10 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/domain/valuerange/ValueRangeCache.java	Removes identity-map support and introduces new of(...) factories for hash-based caching.
core/src/main/java/ai/timefold/solver/core/impl/domain/valuerange/AbstractCountableValueRange.java	Removes isValueImmutable() hook and its documentation.
core/src/main/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/collection/ListValueRange.java	Drops immutability flag usage and builds cache via ValueRangeCache.of(...).
core/src/main/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/collection/SetValueRange.java	Drops immutability flag usage and builds cache via ValueRangeCache.of(...).
core/src/main/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/composite/CompositeCountableValueRange.java	Drops immutability tracking and uses ValueRangeCache.of(int) for dedup/cache creation.
core/src/main/java/ai/timefold/solver/core/impl/domain/valuerange/descriptor/AbstractFromPropertyValueRangeDescriptor.java	Updates construction of SetValueRange/ListValueRange to new constructors.
core/src/main/java/ai/timefold/solver/core/impl/score/director/ValueRangeState.java	Simplifies index map building to hash-based maps (no identity-map path).
core/src/test/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/collection/ListValueRangeTest.java	Adds coverage asserting contains() works across equal-but-distinct instances.
core/src/test/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/collection/SetValueRangeTest.java	Adds coverage asserting contains() works across equal-but-distinct instances.
core/src/test/java/ai/timefold/solver/core/impl/domain/valuerange/buildin/composite/CompositeCountableValueRangeTest.java	Adds coverage asserting contains() works across equal-but-distinct instances in composite ranges.

[triceo]

LGTM when comments resolved.