Migrate no equal then else rule and its tests

[daria-trusca-solid]

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

Changes

• Rule Refactoring: Updated the implementation no_equal_then_else 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 migrates the no_equal_then_else lint rule to the standard analyzer AnalysisRule API, updates its visitor to report diagnostics directly, bumps the SDK constraint, and adds a reflective test suite. The review feedback highlights a critical compilation error in NoEqualThenElseRule where a visitor instance is incorrectly passed to addBlockFunctionBody. To resolve this and prevent inefficient, redundant AST traversals, the reviewer recommends registering specific node processors (addIfStatement and addConditionalExpression) and refactoring NoEqualThenElseVisitor to extend SimpleAstVisitor instead of RecursiveAstVisitor.

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[gemini-code-assist]

The current implementation passes visitor (which is a RecursiveAstVisitor<void>) directly to registry.addBlockFunctionBody. This will cause a compilation error because addBlockFunctionBody expects a callback function of type void Function(BlockFunctionBody), not an AST visitor instance.

Furthermore, using a RecursiveAstVisitor inside a registered node processor is highly inefficient and leads to redundant AST traversals and duplicate diagnostics for nested functions or closures.

Instead, you should register specific node processors for IfStatement and ConditionalExpression directly on the registry. This leverages the analyzer's built-in traversal, making the lint rule much more efficient and correct.

    final visitor = NoEqualThenElseVisitor(this);
    registry.addIfStatement(this, visitor.visitIfStatement);
    registry.addConditionalExpression(this, visitor.visitConditionalExpression);

[gemini-code-assist]

To support registering the visitor methods directly on the registry and to avoid redundant/duplicate AST traversals (double-visiting nested nodes), NoEqualThenElseVisitor should extend SimpleAstVisitor<void> instead of RecursiveAstVisitor<void>.

Suggested change

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