Migrate avoid unnecessary set state rule and its tests

[daria-trusca-solid]

Migrated the avoid_unnecessary_set_state rule and its corresponding tests to comply with the analyzer package.

Changes

• Rule Refactoring: Updated the implementation of avoid_unnecessary_set_state to use the current analyzer syntax.
• Tests: Updated and verified all associated test cases to ensure the rule triggers correctly and no regressions are introduced.

[gemini-code-assist]

Code Review

This pull request refactors the AvoidUnnecessarySetStateRule to extend AnalysisRule instead of SolidLintRule, updating its implementation to use the new analyzer APIs. The associated AvoidUnnecessarySetStateVisitor has been updated to extend SimpleAstVisitor and handle diagnostics reporting directly. Additionally, the PR removes an old test file and introduces a comprehensive unit test suite using AnalysisRuleTest. There are no review comments, so no feedback is provided.

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