Migrate avoid unnecessary return variable rule and its tests

[daria-trusca-solid]

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

Changes

• Rule Refactoring: Updated the implementation of avoid_unnecessary_return_variable 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 avoid_unnecessary_return_variable lint rule to extend AnalysisRule and extracts the return variable usage logic into a dedicated ReturnVariableUsageVisitor. Additionally, the test suite has been migrated to a reflective test structure. The review feedback suggests extending SimpleAstVisitor instead of RecursiveAstVisitor in AvoidUnnecessaryReturnVariableVisitor to avoid redundant AST traversal, which also allows for the removal of a redundant super.visitReturnStatement(node) call.

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[gemini-code-assist]

Since this visitor is registered via registry.addReturnStatement to process specific nodes, it does not need to recursively traverse the entire AST. Changing the base class to SimpleAstVisitor avoids redundant traversal and improves performance.

Suggested change

	class AvoidUnnecessaryReturnVariableVisitor extends RecursiveAstVisitor<void> {
	class AvoidUnnecessaryReturnVariableVisitor extends SimpleAstVisitor<void> {

[gemini-code-assist]

Calling super.visitReturnStatement(node) is redundant when using SimpleAstVisitor and registered via registry.addReturnStatement. Furthermore, it was applied inconsistently as it was skipped in several early return paths. Removing it simplifies the code and ensures consistent behavior.

Suggested change

	rule.reportAtNode(node);
	super.visitReturnStatement(node);
	rule.reportAtNode(node);