Update prefer_equatable_mixin for equatable 2.1.0

[PiotrRogulski]

No description provided.

[Copilot]

Pull request overview

Updates leancode_lint’s prefer_equatable_mixin rule to reflect equatable >= 2.1.0, where Equatable can be mixed in directly (and EquatableMixin is deprecated), while preserving correct behavior for older equatable versions via version-sensitive detection in the analyzer model.

Changes:

• Update prefer_equatable_mixin diagnostic text + auto-fix to recommend Equatable vs EquatableMixin based on whether Equatable is a mixin class.
• Expand tests and mocks to cover both equatable >= 2.1.0 and < 2.1.0 behavior; update missing_equatable_props tests to use with Equatable.
• Update README + changelog and bump package version to 24.1.0.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/leancode_lint/lib/src/lints/prefer_equatable_mixin.dart	Makes the recommendation/fix conditional on whether Equatable is a mixin class (new equatable behavior).
packages/leancode_lint/test/test_cases/prefer_equatable_mixin_test.dart	Adds coverage for both new and old equatable semantics and validates the updated messaging.
packages/leancode_lint/test/mock_libraries/equatable.dart	Introduces separate mocks for equatable >= 2.1.0 and < 2.1.0 to drive version-specific tests.
packages/leancode_lint/test/assert_ranges.dart	Extends range-based assertions to optionally validate diagnostic message contents per range.
packages/leancode_lint/test/test_cases/missing_equatable_props_test.dart	Updates test inputs to use with Equatable (new preferred mixin form) while keeping deprecated mixin coverage.
packages/leancode_lint/lib/src/lints/missing_equatable_props.dart	Updates documentation comment to reflect both Equatable and EquatableMixin mixin usage.
packages/leancode_lint/README.md	Updates rule documentation and examples for equatable >= 2.1.0, including fallback behavior notes.
packages/leancode_lint/pubspec.yaml	Bumps package version to 24.1.0.
packages/leancode_lint/CHANGELOG.md	Adds release notes for the updated lint behavior.

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